Maybe the use of the word sharecropper has changed recently with respect to Apple, but as far as I know, it doesn't have anything to do with whether or not you're successful and content with the Land Owner's restrictions. It's meant to signify that you don't have full control over the ecosystem you're living in and that you owe part of the profits you reap from your hard work to the land owner.

In that sense, App Store developers are very much sharecroppers whether they enjoy and accept it or not.