If it's on top of the desk, it's possibly an "ego purchase".
Most of the time I see Windows "desktop" computers on the floor under the desk - even mini-towers and small-form-factor systems.
Often though, the humongous PowerMac G5 and Mac Pro systems are on top of the desk - like Gucci/Lexus status symbols.
One friend who remodeled his home had a special cabinet built in his office to hid the printer, network connections, file servers and other computer bits - keeping them nicely out of sight.
But his PowerMac G5 (and now octo Mac Pro) is on top of the desk...
Perhaps, but all value arguments aside, Apple really does make the nicest looking computers out there, IMO. Even IT buddies that hate Apple otherwise tell me that.
so why hide it under the desk?