The concept of a refund goes far back in the history of bartering. The concept is simple enough, make a trade you're not satisfied with and you can count on a full or partial refund. Untested or novel products experience greater liquidity when packaged with a reliable refund. There are variations on the refund such as try before you buy, but they offer the same promise.
I've heard the Android mobile app store has had digital refunds in place for some time, but haven't had one long enough to test it out. For Apple's iOS you can call and complain about false advertising or shoddy digital products, but there's no guarantee that you'll receive a refund. Apple embraces Caveat Emptor, or "let the buyer beware".
Historically the cost of providing refunds was higher for physical goods due to shipping and repackaging. There has been and likely always will be abuse of refunds by both sides, angling to renege on the refund due to loopholes or get something for nothing. Yet in a digital age where the costs of additional products are the server bandwidth to deliver it, the rationale not to encourage refunds stands on weak legs.
I can read all the reviews in the world, but until I actually use an application I won't know if it will suit my particular needs. The only reason not to enable refunds is that the company isn't forced to by consumers. Tracking refunds is digital overhead for the host store, but is far from an unsolved problem.
Fellow app buyers, please chime in and correct me if I'm thinking about this wrong but I'd love to have refunds available by default.