As a thought experiment: how many companies would leave the official iOS App Store if offered a choice tomorrow? Epic Im sure... but the experience on Android suggests to me not that many. As with Android, I think a lot will still want a presence on the default/"official" store regardless of the 30 percent take. Don't forget Apple have also done the hard part of getting a customer to enter their CC number to their iCloud account for their store, removing an enormous amount of friction in the sales process too.