Imagination Technologies, owners of PowerVR, recently became members of the Open Handset Alliance four months ago. Open Handset Alliance is the Android booster org. Before this they were a strictly proprietary driver company, and Android devices that used their tech had binary blobs. The binary blobs aren't gone yet, but they soon will be replaced with open source licensed drivers and actual hardware specifications.
So Microsoft needs there to be a mobile GPU tech company that has secret drivers to sell their mobile software on platforms that can't be made useful with a software flash. They cast about and set their sights on nVidia, who has already signed their devil's deal to keep how their PC hardware works a trade secret. They probably promised nVidia something useless to get this - that's their usual course. Now Microsoft's puppet hardware ODMs will build Microsoft nVidia GPU-based tablet platforms that can't run Android, won't sell, and have to be dumped all over the place like Surface RT is now. Expect Surface RT 2, whatever it's properly named, to use this tech. In the end nVidia gets hosed - again. If you sup with the devil, use a long spoon.
Intel used Imagination Tech in their Atom line as well, and that's why you can't get good Linux drivers for those otherwise sweet mini-itx boards. Yet. They're coming. Intel has dropped them though for some reason now in favor of in-house tech.
It's really hard to track the machinations in GPUs.