Semilog is right in that it seems people confuse artifacts and artificial detail as "more detail," which makes AA-less cameras en vogue these days, even to some pros. AA filters are relatively expensive, so it isn't as if most camera manufacturers use them for the heck of it. Of course, as pixel size keeps shrinking, the need for AA filters diminishes, but we're not to that point, yet.
All of that being said, the real advantage of Leica removing the AA filter is in regards to astigmatism with angled light rays. Edge performance, especially with Leica's short registration distance, is improved by removing the AA layer, since it does cause astigmatism leading to softer corners. Leica has to sacrifice moire and false detail for better performance across the frame. Conveniently, this false detail has become known as more sharpness or "sparkle" to many shooters, so it became win-win for Leica.
I don't get moire all that often, but, as Semilog suggests, it is likely because of the nature that I often shoot my M9 (handheld, slight focus errors, lower light, etc.). Throw the M9 on a tripod at F5.6, and moire certainly shows up.
