Thanks for the continued input - all appreciated and noted.
My personal view is that PHP / MySQL / Perl has no place on a .NET webserver, the basic IIS 6 / .NET implementation is a very solid beast and IMHO adding the additional services only compromises the server both resource wise and potentially security wise.
The trouble is many customers seem to want everything and the kitchen sink included (even though they'll never use it) and when comparing plans they'll prefer the one with all the extras quoted on the web site - it's a dilemma for every host.
It's my belief that you keep a faster, cleaner and more reliable server by sticking to the 'pure' MS technologies, part of this research is to ascertain whether a strong enough requirement for a 'pure' MS server exists in the market place.
The point regarding pop3 mail space is an important one and perhaps reflects another difference between Windows and nix hosting in that on most companies open source hosting platforms it's normal for each server to run apache, mysql and smtp / pop locally on the server - this makes it easy for the host to allocate simple block of space for a customer to split how they choose.
In the Windows scenario databases and e-mail are typically on dedicated servers separate from the web servers which is why you get X for webspace X for databases and X for mail - again something that can perhaps be managed through the control panel.
Please keep the suggestions / comments coming - this is proving to be quite an eye opener and I'm grateful for the time your spending on it.