If nothing else, Apple could raise the bar on apps a bit. This would only lower it.
On the contrary, if Apple had more apps to choose from, then it could afford to be more selective. The only thing is that they're already in a position to be more selective, and they're clearly not! (Perhaps too much work.)
That's the point. Apple doesn't need WinMo developers porting their apps to iPhone because a) they are terrible, b) there are not many of them and c) the important/interesting ones are already ported
On the contrary, if Apple had more apps to choose from, then it could afford to be more selective. The only thing is that they're already in a position to be more selective, and they're clearly not! (Perhaps too much work.)