That's the equivalent of saying "We'd like it to work and look exactly the same across every single browser out there" for a Windows application.

It's not a problem writing a Windows application for Win98, .Net 2.0 installs and the programs runs just fine on the OS. The problem is what the client wants the program to do.

A Win98 machine typically has minimal memory, and yet the client wants the UI to look as snazzy as your typical skinned Windows application. So.. no problem I can whip up a skinend application engine, problem is.. what if the user doesn't even have enough RAM to hold all the resources needed to skin the interface?

The worse thing about it is when you try to explain this to the client they just never seem to understand the technical difficulties involved and instead just think the vendor is just trying to worm out of putting more effort into developing the program.