It's pretty simple logic really. Using deferred shading is less costly than not using it, the only problem is that it messes up AA, and getting AA to work with deferred shading is very costly. Given enough time DX10.1 will become the norm. Even if Nvidia is completely successful in getting us to skip over DX10.1, DX11 will eventually become the norm. Since the deferred shading AA issue is fixed in DX10.1 onwards it's only a matter of time before everyone starts using it since it's by far less costly than the alternative. Therefore, it's only a matter of time before you see 4850s outperforming GTX 280s when AA is enabled since they'll only take a fraction of the performance hit.