Things not said from the mausoleum of Steve Jobs:
"We had no idea when we launched the store, the 30% Apple cash grab from developers would be so fruitful... otherwise we would have made it 40!"
The developers are free to charge whatever they like for their apps. If they want to make more money then they can simply increase the price they charge for the app, by more than 30% if they wish. At some point, though, that will result in diminishing returns.
If the developer wants to deny Apple a piece of the pie, then they are free to go elsewhere. If they want to cut EVERYONE else from getting a percentage, then they are free to develop their own ecosystem -- design and manufacture their own smartphone along with its own operating system, continuously revising and improving both, 365 x 24 x 7. Of course then they will also have to make deals with carriers and resellers around the world, which might take a bit of their time. And then they would have to somehow get smartphone users to switch to and buy their new phones.
They might even have a few minutes left over each day to continue working on their apps!