I believe it's the whole mindset of the PC gaming master race. I've had parties with PS3 members, and at first I was surprised because I thought they'd get their own servers, much like with a few cross-over mmos(or dark souls. That's a better example actually). I see no difference in the two and don't understand the elitism that PC users love to rub in console gamers faces so much.
On a personal opinion level, I find using a keyboard for MMOs much more comfortable.
Except when I first played FF11 for the first time a few months ago. THAT WAS FUN.
It took my a few days to finally say screw it to the mouse camera controls and just use a keyboard.