...Well, Mortal Kombat creative director, Ed Boon, doesn't really give a definitive reason as to why there isn't a 360-exclusive character (the PS3 version features God of War's Kratos), but does say that it was something the team wanted to do. According to Boon, he's "not allowed to talk much about it" but tries his best to explain without upsetting the powers that be:
Unfortunately, the circumstances didn't allow us to make a 360 exclusive... I'm not allowed to talk too much about it, but I can tell you we certainly wanted to do an exclusive for 360, but that's all I can say. It was not a decision we made where we said, oh, let's not do one for the 360.
How mysteriously appropriate. So, there you have it, no 360-exclusive character to be found. However, there's plenty of DLC on the way, a couple of unlockable characters, as well as more goodies "hidden deep within the game".
Look for our review of the fighter's return to glory, later this week.