Don't forget that Cave's own online store completely sold out of AK, including those extremely expensive LE sets. The game hasn't price collapsed either in physical or online stores, so it definitely hasn't bombed (unlike DFK, which was reduced in price pretty fast despite having higher MC numbers).
PS/MMP did well enough to get a second shipment for online stores, which is probably a good sign. It's too difficult to rely on MC for 360 titles since most of the niche games are sold online. I sure as hell don't buy them in the stores, they're much cheaper to buy on Amazon and shipping is fast enough. Sure, titles like Deathsmiles and Otomedius chart harder, but they're also a bit more "casual" in design and appeal, so more likely to have stock sold in the stores.