That's very subjective. It's apparent that thousands of developers feel that what they get in return is worth the price. If they don't like the price of goods and services, they can choose not to buy them. They are not on the whole being deprived of anything that is owed to them. It's accepted as "normal" because it's the way commerce works everywhere, and because these are very established practices in fields other than desktop software.
They should be paying developers
They are! Why do you think developers are choosing to develop for these platforms? Where do you think the other 70% goes?