What's stopping Apple is the cost-benefit analysis -- implementing and policing a filtering system to replace the current approval process (especially policing

What's stopping Apple is the cost-benefit analysis -- implementing and policing a filtering system to replace the current approval process (especially policing it) costs Apple more in time, money and complexity than it benefits them. The App Store, like the iTunes store, exists solely to move Apple's hardware. The calculus isn't "will opening up the App Store please the handful of developers who refuse to operate under its current restrictions", it's "will opening up the App Store significantly increase sales of iPods/iPhones/iPads." I have yet to see a convincing argument as to how opening up the App Store would do that.