What they really should add is the ability to try an app for 24 hours. I think they would see sales go up dramatically for apps, I don't buy any software for my PC without trying a demo first, should be able to do the same with my iPhone
Lite versions of the apps let you do just that. Although not all features/levels are available.
Android lets you "return" a full app within 24 hours for a full refund. You don't have to guess if it will do what you need, you can try it and see. I guess you are out 99 cents on your credit card for a day, though, which will probably annoy someone here.
Well they probably would just hold the charge until you've held the app for a day. Otherwise there would be fees for apps that people never kept.