Indeed they are, they currently run games on iOS that were on XBox 360, such as Bioshock. Most games though, aren’t that powerful, and the controls on an iPad... Well, let’s just say it’s more practical to stick to your XBox console or PC for some of the games they are porting portable. No doubt the portable playing is a tribute to power, but using an iphone/iPad screen as an XBox controller is pretty bad.
I’m not a gamer and I avoid using any games at all on the iPad and iPhone, but I do think that the best games are the ones designed for the platform ... and that’s just me observing it “at a distance”.