I used to develop apps for Dan Ariely and we would often chat about this topic. By the latest in psychological research it's less rational than that [1]. Additional factors:

Mental Binning—when we think about buying a $1 app, it doesn’t occur to us to ask ourselves what the pleasure that we are likely to get from this $1 app — or even what is the relative pleasure that we are likely to get from this app compared with a $4 latte. In our minds, those two decisions are separate.

Price Anchoring—we have been trained with the expectation that apps should be free.

1) http://danariely.com/2011/12/25/the-oatmeal-this-is-how-i-fe...