I get where Apple is coming from, though, and it's not just the revenue stream. They want to make sure that if you spent money on something in the Apple ecosystem, you can enjoy that for as long as you got a working device with that app installed. Allowing third-party services like license keys introduce a dependency on the vendor to keep their servers up and running.
Apple wants to make sure they get a 30% cut if you spend money on anything within their ecosystem — that's all they really care about.
There are several reports of people having their entire accounts banned, effectively losing access to everything they paid for. And it's basically impossible to get your account back.
.. well, apart from Apple's own ability to vaporize apps from the store at no notice, and their own upgrade treadmill which tends to cause low-revenue apps to be dropped. No, it's just because someone other than Apple is earning money, and this will probably also end up being overturned.
