Developers won't actually absorb the full discount. A decrease in the fee will force a drop in prices (if that's possible) as developers attempt to find new customers with their newfound margin. If you have a more price-elastic customer base, those customers will reap most of the value of the shift as many will come to enjoy their lower prices.

Secondly, wouldn't this create the perverse incentive for developers of multiple apps to release apps under multiple accounts--some might call them shell accounts--in order to minimize their app taxes?