The Mac App Store previously made up about half of Piezo’s unit sales, so we might have expected to sell half as many copies after exiting the store. Instead, it seems that nearly all of those App Store sales shifted to direct sales. It appears that nearly everyone who would have purchased Piezo via the Mac App Store opted to purchase directly once that was the only option. Far from the Mac App Store helping drive sales to us, it appears we had instead been driving sales away from our own site, and into the Mac App Store… More at Rogue Amoeba.
Obviously you have no choice with iOS apps, but with Mac apps the story is very different. I’m not sure what Apple offers any more for Mac app developers besides an app store that has been severely neglected forever.