They also have to deal with the risk that I don't want to pay them directly and will find an alternative app. I don't think developers understand that many of us want to do business with Apple, not them. Apple provides security knowing that if the developer misleads what their app does I can get refunded.
Ah yeah... there's that...
For the record... I, too, am partial to just letting Apple handle all the payments. I was just looking at it from the standpoint of the developer.
It'll be interesting how much, or if, this will change things in the long run.