Otherwise "auto updates, in-app purchases, and iCloud" (etc.) should be a compelling package to keep developers in line. Not to mention visibility in the store (if they'd bother to provide a useful UI and search, that is).
Apple's antics are well-known, otherwise the situation could be interpreted as some lack of confidence in their own services.
I think they are right; some developers wouuse noose to be different. For example, Adobe would try and use something AIR-based and there would probalby be more than one Linux package-manager-like thing that allows you to get a 'special-for-you compiled executable with exactly the features you want')
That said, the motivation isn't malevolence, it's obsession.
Please look at any Apple quarterly statement. There you'll see that the margins of the app store are in the low single digit percent range, whereas hardware has over 30% or even 40% margins.
That's what Apple is doing both with iTunes and the app store. Which doesn't mean this will always be the model - the rumored Apple TV could be different, there Apple could make most of its money selling services, while selling the hardware at cost. Maybe. Who knows. But the app store, and iTunes are merely feeder operations supporting hardware sales.
Apple has always considered itself an appliance company. They push physical products. That is where they want to generate revenue. Everything else is a means to that end. Debating over how much they make off the app store or iTunes is kinda missing the point.