And of course it's also about controlling quality, are you kidding? Don't reduce this to only being about either one thing or the other — like you apparently love to do — it's obviously a multifaceted issue.
Quality has got to be one of the very primary concerns, Apple would absolutely hate for the iPhone to become a malware infested platform which consumers are afraid to download apps for, always on the look out for viruses, wondering if every unexpected behaviour is the fault of a trojan — like on a certain other platform.
Don't get me wrong, Apple don't just want quality because they're knights in shining armor — they want to make money. And how do you make money? First, make sure your customers feel completely secure and don't hesitate about downloading a new app for even a second. You cannot do that without very high quality apps, distributed in a very secure way. It's not malice, it's a win-win strategy. As has been proven in a plethora of ways.
While the walled garden of AppStore can definitely and be seen as a step backwards, don't you think that the unprecedented amount of apps AppStore makes available for a mobile phone — and the unprecedented amount of developers finally being able to make a living from developing mobile apps — represent a gigantic step forwards?
Once again it's ridiculous to reduce this complex setup to being just one of two things.
Don't be diplomatic. Be open to the fact that things aren't that simple. You'll never understand another's perspective if you don't even make an attempt to.