I think it would be pretty easy for Apple to allow apps to be installed on their devices without having to go through the app store. You can already jailbreak to do this so the capability is there Apple just needs to allow it. Not sure what legal damage you think they would incur except whatever they would pay to fight the suit.
The legal damage would be the fact that each design decision they made around the store would be under court scrutiny.
But so far, you haven't explained why this should be done given that Android offers what you ask for. What's wrong with letting people decide for themselves?
