i.e., providing a way to buy things without giving Apple their 30%.

Maybe Apple is missing an opportunity. If they were to start accepting their 30% in bitcoins, it would sure give that form of payment a boost.

They could, yes. They could require all transactions to go through a wallet they implemented. Or simply require all transactions to send 30% to Apple, though that'd be hard to prove, and would require an even lengthier review process.

But I doubt it's in their best interest to do so, honestly. I'd love it, to be sure, but unless / until Bitcoin gets more acceptance, and makes it past a legal barrier or two, it's high risk and high cost for them.