Well AMD have their own version of FXAA. SSAA exist in AMD drivers and there are various form of AA in AMD that doesn't exist in Nvidia.
The only differences between AMD and Nvidia are AO et AF. You can't use AO on an AMD without an ENB and the AF quality via driver is beter on AMD.
The rest can be put on drivers issues, driver options, monitor parameters or the idiot between the chair and the keyboard :D
That is particulary true with gamma and color when going from AMD to Nvidia (or the other way), you have to recalibrate your monitor.
But I agree, for Skyrim stick to Nvidia.
Speaking of gamma and calibration, Nvidia drivers still don't allow users to force ICC/ICM profiles in games.
And on the subject of additional rendering effects, I don't think it's possible to force FXAA without an injector in AMD drivers (they have MLAA) or various forms of SuperSampling AntiAliasing (such as SGSSAA), which either don't exist in AMD's drivers or don't work with a number of games.
Contrary to popular belief AMD drivers are now very good and provide as much options as Nvidia's. Each constructor has their own proprietary technologies only available via their drivers and sometime in game if they had a partnership with the game developer.
Yes, AMD has their own post-processing AA (not a version of FXAA), and I've already mentioned it in my previous post. SuperSampling on AMD cards doesn't work in every game, NVIDIA has better support for a few engines out there. And you certainly can't enabling anything like SGSSAA in Skyrim on AMD cards. Even though their own SSAA method works OK.
However, contrary to what you have said before, AMD graphics cards can use Ambient Occlusion with RadeonPro. See the post below.