It was arguably Namco that started the whole 'exclusive character per platform' trend that's hit a number of games since Soul Calibur II. Sega's upcoming videogame based on the Robert Downey Jr. Iron Man movie is the newest game to feature platform exclusive content. Specifically, the Xbox 360 and PlayStation 3 versions will feature an additional extra Iron Man suit each.
The Ultimate suit (PS3 exclusive) is the suit Iron Man wears in the Ultimate Universe, and its capabilities are more complicated than that of the Mark III. The suit also doesn't function to keep Stark's heart beating, but rather to diminish a pain that grasps his body and the suit was actually made by his father. The suit acts like symbiote, as it can regenerate and dissolve metals, among performing other unusual functions.
The Silver Centurion (Xbox 360 exclusive) suit is actually just a collage of prototype all rolled into one. The cool thing about the SC suit is its ability to cast a force field and expel magic, or use its magnetic traits to attract it. The suit was specifically created and put to use in order to defeat Obadiah Stane, after Stane had nearly destroyed Stark during a previous bout. The Centurion armor proved to be successful.
We have to admit that we're more partial to the look of the Ultimate Suit, as it looks a lot sleeker and more in line with the Mark III and some of Starks' other creations. Sega has made no mention on whether or not we'll be given the ability to use each suits unique powers, but somehow we doubt it. The bonus suits are likely just skins, where as the Mark I, Mark II, and Mark III will all boast different capabilities.