The bottom line is you can use more software sharpening to regain a sharp image with a AA filter inplace but images look more realistic/better with less software sharpening and no AA filter. I think this is one reason MFDB images look so good. The question remains is it worth $450? On my 5D I think it was worth the $ on my D80 it was not. On a 1Ds III yes I would do the mod.
This topic comes up from time to time, with writers always suggesting, implicitly or explicitly, that camera manufactures who include (or omit) an AA filter don't know what they are doing. Nonsense! Particularly with cameras using a Bayer-type sensor, careful attention must be given to matching the digital sampling of the sensor and the resolution of the lens. It is instructive to consider two case -- 1. the 3MP sensor and 2. the 3000 MP sensor (at least conceptually ). In the first case, most would agree that aliasing would be a severe problem and it would likely affect all images, not just the ones with repetitive patterns. In the second case, it is likely that the sensor would not exhibit any noticible aliasing because of the high spatial sampling. Put another way, the Nyquist frequency equivalent for the sensor would be higher than the Nyquist frequency for the lens. So, it is this balance between sampling and lens resolution that must be properly struck. The AA filter is supposed to limit the high frequency information passed by the lens so that the image can be "reconstructed" up to the Nyquist frequency. Fabricating a perfect AA filter is apparently a problem. Too strong and you loose resolution you are entitled to and too weak leads to aliasing and Moire patterns. It has to be just right! Notice that with a Bayer sensor, the poorer sampling of red and blue can lead to problems. High quality lenses can be a problem for lower MP DSLRs made without a proper AA filter.
Contrary to assertions made in this thread, there is no general algorithm capable of undoing Moire or aliasing. Aliasing puts high frequency details in the wrong place in the image. Without detailed apriori knoweldge of the scene it can't be corrected, though perhaps it can be mitigated in some cases.
As a speculation, I suggest that cameras like the 1DsIII may be reaching the point where they would function well without an AA filter for all but the best lenses.