The difference between the two keyboards is integration and additional hardware (mixer, 172 dedicated buttons, builtin MIDI chips etc).
The Mediastation is an integrated keyboard (just like traditional keyboards) where you do not need to fiddle around with a mouse on a windows XP desktop.
Of course if you want to use it witha mouse and keyboard you can do so but you are not required to do so.
Just ask how many live players would prefer a windows desktop to a traditional keyboard user interfaces. (LCD, possibly large and lots of dedicated buttons, dials, sliders and knobs).

And ask them too how much they trust Windows in a live music enviroment.

I'd be curious about the result of such polls.
;-)

cheers,
Benno