>Can anyone think of a clear, unambiguous rule that would allow things like Dropbox, Skydrive, Amazon, etc. to get around the 30% fee, but without allowing loopholes that would allow everyone to skirt it?
Simple: alternative stores should be enforced by law. Apple alone deciding what goes onto iDevices is wrong. (Ditto Microsoft with WP). Let the market decide.
And hasn't the market decided? Users are buying both Android and iPhone devices, and to a far lesser extent WinFones. Since Android has far higher market share than Apple, it seems like this should be perfect. Yet for people who are actually buying apps online, Apple seems to be doing quite well.
Perhaps you're idea of letting the market decide isn't really focused on the market so much as developers...
Simple: alternative stores should be enforced by law. Apple alone deciding what goes onto iDevices is wrong. (Ditto Microsoft with WP). Let the market decide.