From an entrepreneur's perspective, devoting one's business solely into the app store isn't a wise move. Since Apple has the veto power over the app distribution channel the risk of wasting hundreds of hours but not getting to the market is too high.
What one should do is to develop software that runs multiple platforms, and if it becomes popular I doubt Apple would want to lose out in the fanfare.
Imaging Apple disapproving Dropbox? not quite possible, because people love it on other platforms, and if Apple doesn't support it on iPhone people will go get a blackberry.