You're assuming a developer would have bothered submitting such an app to Apple's store in the first place or hasn't tried to already. The reality right now is

You're assuming a developer would have bothered submitting such an app to Apple's store in the first place or hasn't tried to already. The reality right now is that many people just give up because of either Apple arbitrarily banning things for opaque reasons, Apple banning things because they compete with Apple, or because it's not economical enough to be worth the effort (the other effect of high commission rates, not only do users end up paying more for apps that are available, but it causes some apps to never exist). This also assumes that Apple won't make their store more friendly to developers once they have competition... i.e that app that would have never existed could now exist in Apple's store because they are forced to actually compete. As I said - indirect benefits.