Exactly. Apple takes a 30% tax and one says anything?
However, this isn't an apt comparison to what Adobe's doing. Apple, Google, Amazon, etc provide the infrastructure, hosting, payment processing, and the integration into the device. Adobe is providing none of this, yet is still claiming a piece of the action.
The guys that do it, do it because they can.
When GOOG and AAPL first launched their stores, it they were clear in saying they were going to take 30% (hosting/banking/whatever they justified). If you had a successful product with Adobe that was running for over a year using their "premium" libraries, you just lost 9%.