It seems that the AMD 6750 and 6770 GPU is only supported on the MacBook Pro vs. the same GPU on the iMac. How does that work .. as its the same GPU?
AMD Radeon HD 6770M (only on MacBook Pro computers with OSX 10.7.x with minimum 1GB VRAM)"
Believe it or not, the MacBook Pro has a slightly different GPU than the iMac. We didn't have enough bandwidth to test and certify the GPUs in iMac for CS6. Feel free to request that feature: http://www.adobe.com/go/wish
AMD Radeon HD 6770M
The M designation stands for Mobile (meaning Laptops). They are often different than their non-M siblings.