People are probably more embarrassed to ask for their money back on something they have partially or entirely eaten. I can barely muster up the courage to tell my waiter that my dinner order wasn't quite right but I have zero problem with buying a couple different versions of a product and returning the ones I don't like.
That's interesting - I hate wasting food, I have never complained about my order (and not planning too, unless the food is spoiled I guess). If I don't like the food, I'll just never order again from the same place. I would definitely appreciate a company that offers money refund on food "no questions asked" even if I was never going to use it - it shows respect.