Developers are actively leaving the App Store - Panic pulled their popular Coda web development app & recommended customers switch to the version from their own site. The sandboxing requirements of the App Store made many of Coda's features impossible to implement in the App Store, plus Apple had to approve all updates & took a 30% cut (compared to about 2.6% for a direct credit card transaction).

They say after they left the App Store, their revenue went up 44%:

https://www.panic.com/blog/the-2014-panic-report/

"I was pretty nervous to be pulling Coda from the Mac App Store. But when we finally did it, I felt an incredible, almost indescribable sense of relief — mostly because as we began to wrap up bug fix releases, we were able to immediately post them to our customers within minutes of qualifying them. My god. That’s how it should be. There’s just no other way to put it — that’s how you treat your customers well, by reacting quickly and having total control over your destiny. To not be beholden to someone else to do our job feels just fantastic. (Also to not pay someone 30% in exchange for frequent stress is a fine deal.)"