how do web hosting companies give ssh and root to so many users.

[Abhishek Dixit]

Hi,
it may not be the right list for this question so please consider my
apologies for that.The reason I am posting here is I feel the people
on Ubuntu server list are quite knowledgeable and will be able to
answer my question.I have been trying to understand this from quite
some time LQ,Serverfault, and many other forums I asked this question
but I am not satisfied with the answers that I got so asking here.I
want to know how do these web hosting companies give the end user (who
is their customer) the root access to the server.Where do so many IPs
come from and how is it possible that each customer who is given a
root access is able to gain root access.If I were to do the same let
us take a situation I have a public IP and a big server farm behind
that.
So if I have to give people from internet SSH access to those machines
behind my public IP in my server farm
then on the main machine in its .ssh/config I will configure a Proxy such as

  ProxyCommand ssh a nc -w 3 %h %p


So that I give the end user in one step a console to an internal
machine.That is one mechanism which comes to my mind or create some
sort of tunnel and then give a GUI to that SSH tunnel.
But what I have seen people doing is
ssh user@<IP given by hosting company>
and they directly login at port 22 and no tunnel or ProxyCommand (in
my opinion) is used there.

I don't think that above sort of Proxy configuration is used in such
scenarios.But the curiosity I have is how come these Web Hosting
Companies have so many public IPs and even if they have then how do
they actually manage root logins to each of these machines.Maintenance
of such a system would be extremely complex in my opinion.
Also no one seems to be using Apache Reverse proxy at the Hosting
level so how do these companies actually make this possible,
I am looking from a technical perspective.I am an experienced sys
admin kind of guy who knows Linux but never worked with a Hosting
Company.
Any link to some good doc which can satisfy my curiosity will be
greatly appreciated.

-- 
Regards
Abhi