Well, the coffee has a marginal cost that is non-trivial. Downloading an app has essentially zero marginal cost.
Its like the lock-smith who slaves for an hour using a dozen tools vs. one who takes 30s and no tools. The latter is more skilled and served you better but will not feel as valuable. The artificial scarcity of an app and the work of "not preventing you downloading something" just doesn't ring our value bell.
If I download a $2 app I might get lucky and use it right away in which case it might be a great value. Or it might require 30 minutes of setup and experimentation in which case it has already cost me more than the coffee.