sources.list strange behaviour

[Nick Darby]

After getting a couple of errors consistently with UK (gb)sources I
decided to change to the Netherlands (nl), and my new source.list is:

# Automatically generated sources.list
# http://www.ubuntulinux.nl/source-o-matic
#
# If you get errors about missing keys, lookup the key in this file
# and run these commands (replace KEY with the key number)
#
# gpg --keyserver subkeys.pgp.net --recv KEY
# gpg --export --armor KEY | sudo apt-key add -

# Ubuntu supported packages (packages, GPG key: 437D05B5)
deb http://nl.archive.ubuntu.com/ubuntu dapper main restricted
deb http://nl.archive.ubuntu.com/ubuntu dapper-updates main restricted
deb http://security.ubuntu.com/ubuntu dapper-security main restricted

# Ubuntu supported packages (sources, GPG key: 437D05B5)
deb-src http://nl.archive.ubuntu.com/ubuntu dapper main restricted
deb-src http://nl.archive.ubuntu.com/ubuntu dapper-updates main
restricted
deb-src http://security.ubuntu.com/ubuntu dapper-security main
restricted

# Ubuntu community supported packages (packages, GPG key: 437D05B5)
deb http://nl.archive.ubuntu.com/ubuntu dapper universe multiverse
deb http://nl.archive.ubuntu.com/ubuntu dapper-updates universe
multiverse
deb http://security.ubuntu.com/ubuntu dapper-security universe
multiverse

# Ubuntu community supported packages (sources, GPG key: 437D05B5)
deb-src http://nl.archive.ubuntu.com/ubuntu dapper universe multiverse
deb-src http://nl.archive.ubuntu.com/ubuntu dapper-updates universe
multiverse
deb-src http://security.ubuntu.com/ubuntu dapper-security universe
multiverse

>From a terminal I get:

nick at Nicksamesh:~$ sudo apt-get update
Get: 1 http://gb.archive.ubuntu.com dapper-updates Release.gpg [191B]
Get: 2 http://security.ubuntu.com dapper-security Release.gpg [191B]
Get: 3 http://nl.archive.ubuntu.com dapper Release.gpg [189B]
Get: 4 http://nl.archive.ubuntu.com dapper-updates Release.gpg [191B]
Hit http://gb.archive.ubuntu.com dapper-updates Release
Get: 5 http://nl.archive.ubuntu.com dapper-backports Release.gpg [191B]
Hit http://security.ubuntu.com dapper-security Release
Hit http://gb.archive.ubuntu.com dapper-updates/main Packages
Hit http://nl.archive.ubuntu.com dapper Release
Hit http://security.ubuntu.com dapper-security/main Packages
Get: 6 http://gb.archive.ubuntu.com dapper-updates/restricted Packages
[14B]
Hit http://gb.archive.ubuntu.com dapper-updates/universe Packages
Hit http://nl.archive.ubuntu.com dapper-updates Release
Hit http://security.ubuntu.com dapper-security/restricted Packages
Hit http://security.ubuntu.com dapper-security/universe Packages
Hit http://security.ubuntu.com dapper-security/multiverse Packages
Hit http://nl.archive.ubuntu.com dapper-backports Release
Get: 7 http://gb.archive.ubuntu.com dapper-updates/multiverse Packages
[14B]
Hit http://gb.archive.ubuntu.com dapper-updates/universe Packages
Hit http://nl.archive.ubuntu.com dapper/main Packages
Hit http://security.ubuntu.com dapper-security/main Sources
Hit http://security.ubuntu.com dapper-security/restricted Sources
Hit http://security.ubuntu.com dapper-security/universe Sources
Hit http://security.ubuntu.com dapper-security/multiverse Sources
Hit http://nl.archive.ubuntu.com dapper/restricted Packages
Hit http://nl.archive.ubuntu.com dapper/universe Packages
Hit http://nl.archive.ubuntu.com dapper/multiverse Packages
Hit http://nl.archive.ubuntu.com dapper/main Sources
Hit http://nl.archive.ubuntu.com dapper/restricted Sources
Hit http://nl.archive.ubuntu.com dapper/universe Sources
Hit http://nl.archive.ubuntu.com dapper/multiverse Sources
Hit http://nl.archive.ubuntu.com dapper-updates/main Packages
Hit http://nl.archive.ubuntu.com dapper-updates/restricted Packages
Hit http://nl.archive.ubuntu.com dapper-updates/universe Packages
Hit http://nl.archive.ubuntu.com dapper-updates/multiverse Packages
Hit http://nl.archive.ubuntu.com dapper-updates/main Sources
Hit http://nl.archive.ubuntu.com dapper-updates/restricted Sources
Hit http://nl.archive.ubuntu.com dapper-updates/universe Sources
Hit http://nl.archive.ubuntu.com dapper-updates/multiverse Sources
Hit http://nl.archive.ubuntu.com dapper-backports/main Packages
Hit http://nl.archive.ubuntu.com dapper-backports/restricted Packages
Hit http://nl.archive.ubuntu.com dapper-backports/universe Packages
Hit http://nl.archive.ubuntu.com dapper-backports/multiverse Packages
Hit http://nl.archive.ubuntu.com dapper-backports/main Sources
Hit http://nl.archive.ubuntu.com dapper-backports/restricted Sources
Hit http://nl.archive.ubuntu.com dapper-backports/universe Sources
Hit http://nl.archive.ubuntu.com dapper-backports/multiverse Sources
Fetched 33B in 0s (92B/s)
Reading package lists... Done
W: Duplicate sources.list entry http://gb.archive.ubuntu.com
dapper-updates/univ erse Packages
(/var/lib/apt/lists/gb.archive.ubuntu.com_ubuntu_dists_dapper-upda
tes_universe_binary-amd64_Packages)
W: You may want to run apt-get update to correct these problems

nick at Nicksamesh:~$ sudo aptitude update
Password:
Reading package lists... Done
Building dependency tree... Done
Reading extended state information
Initializing package states... Done
Building tag database... Done
Get:1 http://gb.archive.ubuntu.com dapper-updates Release.gpg [191B]
Get:2 http://security.ubuntu.com dapper-security Release.gpg [191B]
Hit http://security.ubuntu.com dapper-security Release
Hit http://gb.archive.ubuntu.com dapper-updates Release
Get:3 http://nl.archive.ubuntu.com dapper Release.gpg [189B]
Get:4 http://nl.archive.ubuntu.com dapper-updates Release.gpg [191B]
Hit http://nl.archive.ubuntu.com dapper Release
Hit http://security.ubuntu.com dapper-security/main Packages
Hit http://gb.archive.ubuntu.com dapper-updates/main Packages
Hit http://nl.archive.ubuntu.com dapper-updates Release
Hit http://security.ubuntu.com dapper-security/restricted Packages
Hit http://security.ubuntu.com dapper-security/main Sources
Hit http://security.ubuntu.com dapper-security/restricted Sources
Hit http://gb.archive.ubuntu.com dapper-updates/restricted Packages
Hit http://gb.archive.ubuntu.com dapper-updates/universe Packages
Hit http://security.ubuntu.com dapper-security/universe Packages
Hit http://security.ubuntu.com dapper-security/multiverse Packages
Hit http://security.ubuntu.com dapper-security/universe Sources
Hit http://security.ubuntu.com dapper-security/multiverse Sources
Hit http://gb.archive.ubuntu.com dapper-updates/multiverse Packages
Hit http://gb.archive.ubuntu.com dapper-updates/universe Packages
Hit http://nl.archive.ubuntu.com dapper/main Packages
Hit http://nl.archive.ubuntu.com dapper/restricted Packages
Hit http://nl.archive.ubuntu.com dapper/main Sources
Hit http://nl.archive.ubuntu.com dapper/restricted Sources
Hit http://nl.archive.ubuntu.com dapper/universe Packages
Hit http://nl.archive.ubuntu.com dapper/multiverse Packages
Hit http://nl.archive.ubuntu.com dapper/universe Sources
Hit http://nl.archive.ubuntu.com dapper/multiverse Sources
Hit http://nl.archive.ubuntu.com dapper-updates/main Packages
Hit http://nl.archive.ubuntu.com dapper-updates/restricted Packages
Hit http://nl.archive.ubuntu.com dapper-updates/main Sources
Hit http://nl.archive.ubuntu.com dapper-updates/restricted Sources
Hit http://nl.archive.ubuntu.com dapper-updates/universe Packages
Hit http://nl.archive.ubuntu.com dapper-updates/multiverse Packages
Hit http://nl.archive.ubuntu.com dapper-updates/universe Sources
Hit http://nl.archive.ubuntu.com dapper-updates/multiverse Sources
Fetched 4B in 0s (8B/s)
Reading package lists... Done
nick at Nicksamesh:~$

Why does the gb archive still appear? and whats the difference between
apt-get and aptitude?
Thanks in advance for any enlightenment!!
Nick