It's not preventing other stores period. It's preventing other stores in their store. You're arguing against a point I didn't make.
It is anti-competitive to prevent competing stores. How you do it is irrelevant.
and their OS. I don't care if they allow whatever on their store. I would like the option to go to other stores or even sideload my own apps without the store intervention. That's right now impossible without a) hacking the device or b) being a dev working on an app.