I don't think $100 is enough of a disparity to get the market we're talking about even vaguely interested. Especially since the titles we're talking about (I think we're talking about stuff like the Modern Warfare games) simply aren't feasible on an ARM proc yet.
That's a really interesting question, but I don't think Apple's going to be the company to take gaming in that direction. Their cloud services are pretty lackluster. I have an ATV, and I only ever use it for Netflix streaming.
They're already there, all you really need is the ability to stream H.264 and monitor input events. What isn't there is consumer internet connections, most people won't be able to have an enjoyable experience.
