Yeah, I can see that happening. Looking through my purchase history on my Mac and iPad - there are a handful of apps that I've purchased for one specific use, or are only useful for a limited time (ie, a fantasy football draft application). In all cases, I feel like I got my $1 worth, but if the feeling is "eh, I'm not going to use this anymore", there isn't any incentive to go through the process of paying for it.

Depending on how this is implemented and whether or not it is optional, it could be problematic for some useful apps.