You should look at what Carmack is doing with Tech5 ... built from the ground up to be a multiplatform engine (think of what he did with Tech4 having individual renderers for each GFX card around the time only now for platforms).
I think the idea of exclusivity to platforms impacting graphics has just had the first nail put in its coffin, sure there is the drawback of it taking most other developers the best part of a decade to catch up with Carmack's engine design philosophies, but they will get there eventually.
