Well, the 6970 does have some other things going for it, the coolest of which is the dual BIOS. It has two BIOS chips, one of which cannot be modified. You can change the other one to anything you want, play with the default overclocking/voltage settings, etc. If something goes wrong, it copies the other one back in, effectively resetting it to the factory BIOS. Pretty cool. It's also is capable of Eyefinity, where you can run three monitors off of one card.
That said, Nvidia has market dominance right now, which a fair few games are coded to work better with their hardware...those are the ones where it takes the lead in. It also has CUDA, which again, is coded for a lot more than ATI Stream due to Nvidia's market dominance. Not really relevant unless you're doing heavy media editing or something, though. Nvidia also seems to do a better job on their drivers.