There is also a class of apps that Apple finds objectionable for reasons outside of private API usage. This is my favorite recent example:

http://www.theregister.co.uk/2015/11/02/apple_clubs_chaos_co...

In addition, people underestimate what you can do from the sandbox (and will be able to do for a long time, unless Apple speeds up its development cycle): https://news.ycombinator.com/item?id=10415288