* Some level of guarantee that every app on my phone has been vetted (it's not perfect of course, but is better than nothing). It's unlikely that anything to nefarious makes can make it onto my phone, and if it does, it'll be removed.
* I get a better fit and finish. Apps on the iPhone very often have a better quality to them.
* I get the ability to refund when needed.
* Personally, my support requirements go down. When my nephew calls me with a problem, I know that he didn't go download some random app from instructions he got from a friend.
Clearly, there's also some profit in there.
Edit: Perhaps to get to my point -- these were ALL known when I bought my phone, and for me, were part of the reason I bought it. If I was not ok with this, I would have bought an Android phone.