I presume this is more a deal of convenience and extra income. Intel's integrated grahics are doing pretty well - AMD want one of their own. Partner up with an effective GPU maker, who can still manage the graphics side proiftably, and develop some combined development for CPU+GPU combos, especially for the likes of portables, and it's good to go all round. Other offers to work with ATi would probably come on a per-basis consideration. If IBM wanted to work with ATi for integrated CPU+GPU, they might come unstuck, but it'll likely be business as usual elsewhere.
And I do see parallels with the nVidia+Sony talk of wanting to work closely together. Are we approaching the age of integrate processors rather than discrete processors (the opposite of PCs with CPU, GPU, PPU and audio)? A future of devices that all one big pool of RAM and one processor that can turn it's hand to graphics, computing, and everything else, would make for a simple system for devs. I can see it's appeal.