"The 360 was running deferred rotated grid super-sampling for the last two years, but later we switched it to use analytical anti-aliasing (AAA)," reveals Shishkovtsov. "That gave us back around 11MB of memory and dropped AA GPU load from a variable 2.5-3.0 ms to constant 1.4ms. The quality is quite comparable. The AAA works slightly different from how you assume. It doesn't have explicit edge detection.
"The closest explanation of the technique I can imagine would be that the shader internally doubles the resolution of the picture using pattern/shape detection (similar to morphological AA) and then scales it back to original resolution producing the anti-aliased version. Because the window of pattern detection is fixed and rather small in GPU implementation, the quality is slightly worse for near-vertical or near-horizontal edges than for example MLAA."