Because - at least in Apples case - customer and developers have no alternative and no choice. There isn't a market setting a fair price for Apple's "service". You can't get on iPhones (for which people paid already!) without the App Store. You aren't asked if you want to pay for that "service" and there aren't any competitors. If you want to have an app, Apple owns 30% of your business, even if they didn't generate you a single installation.

This is the same as with store owners who have to hand over part of their earnings as danegeld to some gangs controlling their neighborhood. They also pay happily for a great "protection" service. Would be a pity if something happens to your nice store (or app, in Apples case)!

I don't get how anyone who stands up for freedom of information, a free internet and a fair economy can still own an iPhone without developing schizophrenia..