As far as I can see, what distinguishes Apple from Google is status quo. Apple never did allow app distribution other than through the Apple App Store. i.e. "We've always been doing it"
That's what I'm getting at. Is it anticompetitive to deliberately make your product worse by removing a key differentiator between your product and its closest competitor?
Or come at it from another angle: would it be "anticompetitive" for Apple to (in new iPhones) completely remove the App Store and thus all reasonable expectation to be able to run third-party software? Is it anticompetitive to sell a handheld computer than can do email, play music and videos, etc., but not run third-party software?