It's quite obvious from rendering a model that anti-aliasing destroys very fine details in normal mapping. Is this why most games support only 2x and 4x? Is it more common to simply anti-alias lines instead?

The common form of antialiasing (MSAA - Multisample Antialiasing) does not affect textures or normal maps. They only affect geometry edges. Supersampling will affect the entire scene, which is a very good thing since it also antialiases shader effects such as normal maps. Supersampling is very expensive, though. So I don't know why you think that details in normal maps would be "destroyed".

Most games only support 2x and 4x because that's pretty much the lowest common denominator. Both AMD Radeon and Nvidia Geforce card support 2x and 4x MSAA. Radeons support an additional 6x mode, and Geforce cards support an additional 8x and 16x mode. More recently, several other AA modes have been added to various DX10-level video cards, but 2x and 4x remain as the standard since everything supports it.

I have a feeling the OP might be refering to texture filtering, or possibly mip mapping. If he is talking about anti-aliasing though... what SC4Freak said..

Alright, Thanks. I didnt know multisampling was strictly edges.