Do they contribute back as much as they should, ethically?
I don't understand why this nonsense gets modded up. Apple is under no ethical obligation to contribute anything to open source. They are under a legal obligation to contribute to open source software in specific circumstances, such as in the case of distributing of modified GPL software. Its complete bullshit to expect any company or person to go above and beyond the legal obligations of using open source software, even if that software is helping them bring in heaps of cash.