It's conceivable, of course, that Apple would offer gaming downloads from the iTunes Store that could play on the iTV -- and I certainly hope they turn the iTV in a family/home server for files and home folders as well as for multimedia. But it seems unlikely that the iTV would be engineered to kill other gaming boxes...not when the real trick is going to be pushing high speed data through the thing and decompressing data feeds into video streams. Those are core competencies for Apple, whereas, as of right now, gaming APIs and high-end graphics card support isn't.
Of course, they might be working all that stuff in secret, but why jump into a cut-throat market like console gaming when there are entire pioneer markets waiting for an easy, reliable, downloadable movie solution?