With Coffee you know what you are getting and know that at a minimum it will supply enough caffeine to give you a mid-morning perk. Almost all coffee shops provide coffee that is consistently good enough that it won't taste disgusting so the process is an evolutionary one, if you find a better coffee shop that is only slightly further away you will just go there from that point on.
The problem with buying apps, especially on mobile stores is that I've bought several (even well rated ones) that either do not work at all on my device or are close to useless for my purposes. Since many apps don't offer trials and the android store return policy doesn't give you enough time often to make an informed decision of whether or not to keep an app you do have to do your homework or you risk throwing $2 away.
$2 isn't allot of money but it is for something which is 0 use to me, a $4 coffee even if it's not the most delicious will at minimum provide a caffeine fix. I can think of a few occasions on the android market where I have spent $10-15 just buying a variety of $2-5 apps that supposedly do the same job in order to find one that I actually want to use. I can reduce this cost significantly by doing some research although an hour would seem excessive in most occasions 15-20 minutes may be reasonable.