Do you know what? I bet B&N tested this in front of a focus group. I bet that B&N asked what was the least attractive feature, and after the focus group complained about the locked down nature of the Nook platform I bet B&N ignored them (what do customers know, anyway) and then B&N decided that what the customers really wanted was in-app purchases.
Never mind that the Nook App Store still has fewer than 10,000 titles, a number which is best termed as pathetic when compared to iTunes, Google Play, or even the Amazon Appstore (50k apps as of Sept 2012).
Barnes & Noble is probably expecting this to boost revenue, but one thing they seem to have forgotten is that hardly anyone is buying Nook hardware. Maybe B&N should do something about that first? I don't know, maybe B&N could give customers a reason to pick Nook hardware over competing Android tablet.
B&N could, for example, allow customers to install Android apps downloaded from other websites. But this is probably something B&N will never do (they want to profit from their captive app store).