I think Sony made the right decision there. If Microsoft approached me about "co-operating" I wouldn't touch them with a 10 foot pole. Look how well it worked out for IBM (with MS-DOS and OS/2) or Sun (with Java).
You only have to see how Toshiba's "cooperation" with Microsoft worked out for them with HD DVD to see what a bad idea it could be. Nokia could be the next victim of that "cooperation".
The greater challenge would be architecting the game or app to make use of the cells in an optimal way and to move as much logic as possible into them to free up the CPU for other tasks. I expect cross platform games have it even harder since they have two opposing goals - to make the game work optimally across platforms and to share as much code as possible. Wouldn't be surprised if some of them have developed a higher level language which allows the logic to be expressed once and transformed to the equivalent code for use on 360 or PS3.
I recall the exact same BS coming from Linux zealots a 10 years ago - buy a Zaurus it runs Linux!!! Yes it did and the device was still an expensive, battery sucking, heap of shit compared to a Palm or even a Windows Mobile devices of the same vintage. Palm devices especially were popular not for the prowess of the kernel but because they actually did what they were built for.
It is better to give than to lend, and it costs about the same.