not sure on numbers for each platform - but it was the fastest selling game last year on all platforms. Plus and minus for each platform, so no "my version is better than yours"...
No you cant play cross platform games from Xbox / PS3 or PC - nice idea, but some platforms there is no subscription and plus I cant see Sony @ MS playing nicely since they are direct competitors with the own platforms
I'm afraid the game makers IW have ruined the pc version not having dedicated servers, it was the pc gamers who made cod into what it is today from call of duty 1 and so on. Obviously pc sales getting smaller so they spend less time and effort on it. I have it for pc and xbox 360 the 360 version in terms of enjoying is poor compared to the pc. But the fact of the matter is the majority of sales for the game will be kids who can't afford a £600 gaming computer and thats minimum you would need to spend to run it on good settings but they can afford a portable t.v and £150 xbox 360 so I would say the most popular platform by far would be the consoles;
A shame really because no FPS can be played at the same pace and have the same amount of realism in my opinion as a PC version for any game.
£150.00 - £250.00 to play on a console that will work for all users compared to £600+ for a pc version that may or may not perform as well as a similar spec / price machine using a different mobo or RAM etc.
PC gaming is sadly in decline - simply because to get the best experinece you need a high spec pc for some of the most recent games - even then some still struggle with the likes of Crysis.
Its a shame really because as much fun as console gaming can be, its gaming that drives forward a lot of PC development.