My full time job as an iOS developer is for a company that makes 100% of its income from app purchases. Mostly up front (our app is a plain old paid app), but we do have a couple in app purchases for optional extra "pro" features.
That was true of my last developer job too, where I was (primarily) a Mac developer. There, most of our sales were direct, ie. not on the Mac App Store (we did have some MAS income).
That said, it's pretty hard to become successful through app store sales alone, and you definitely can't rely solely on the app store to do your marketing, promotion, etc. The app store is a distribution channel, and if you get lucky, you can get promotional value out of it, particularly if Apple features your app, but it doesn't replace traditional marketing strategies.
That was true of my last developer job too, where I was (primarily) a Mac developer. There, most of our sales were direct, ie. not on the Mac App Store (we did have some MAS income).
That said, it's pretty hard to become successful through app store sales alone, and you definitely can't rely solely on the app store to do your marketing, promotion, etc. The app store is a distribution channel, and if you get lucky, you can get promotional value out of it, particularly if Apple features your app, but it doesn't replace traditional marketing strategies.