That's not correct, this setting only applies to alpha textures and the amount is determined by how many msaa samples you're using.
To enable true supersampling you need to download nhancer from here:
http://www.nhancer.com/
You can then choose from a range of supersampling and (my favourite) "combined" supersampling/multisampling aa modes and apply them on a per game basis.
Combined 2x2 supersampling w/ 4xmsaa w/transparency multisampling is damn nice looking and the performance hit isn't
too great at 720p with modern GPUs, quite a few games will run with this setting just fine.
You can also try "options > enable experimental modes" in nhancer to get access to some new multisampling modes including the infamous quincunx (of PS3 fame) and 4x9Tap which is a similar algorithm to quincunx only for a 4xmsaa application and the results are generally better.