[ec2] Difference b/w UEC ubuntu server and destop server

[Lal]

Dear list members,

The page http://uec-images.ubuntu.com/releases/karmic/alpha-4/ says,

"The images published here are ready-to-run versions of Ubuntu Server
for Ubuntu Enterprise Cloud (UEC) or Amazon EC2."

I understand, these are Ubuntu Server images which can be run remotely
using UEC.

Am I right to understand these images as AMI (Amazon Machine Image) ?

How these images are different from Desktop Ubuntu (Server) ? A few
examples (of technical features) would be appreciated.

Thanks
-Lal