I want to write deep, usable applications that have a shelf life of more than a few months. It can take years for an update to come out (hello VoodooPad 5!) and while the warm fuzzy feeling when folks love your application more is great, it doesn’t really feel the same as being able to make a living off your work.
Trials and paid upgrades are things I’d like to see in the App Store as a consumer. I believe they are needed to support applications with deep functionality. The current model of “buy everything and see what works” just doesn’t jive for me. Perhaps I have too much old school baggage.