The PlayStation 3 version of Mortal Kombat
has Kratos. The 360 version? Nada. It's not NetherRealm's fault though.
Ed Book talked with Eurogamer
and said he isn't allowed to talk about why there isn't an Xbox 360 exclusive character. They really wanted to do one and the names of Master Chief and Marcus Fenix were brought up.
I'm wondering why Microsoft would say no unless, of course, they want to make a DLC and grab some more money out of it. Wouldn't surprise me, but maybe someday we'll get an answer as to why there isn't an exclusive character on the Microsoft console.