There's nothing abnormal to working on multiple branches of software releases. 10.8.1 is probably in a feature freeze and now any new features or "bug" fixes that require more important changes in the code that can impact functionality are being moved to the 10.8.2 branche instead.
This is pretty much normal practices in the industry, where you have your current branch where you continue actively working on adding features and doing bigger fixes and clean ups and your beta branch that keeps getting some smallish fixes in order to get a release out.
I don't quite understand why you're shocked by this.
It's fairly certain that Apple is also working on 10.9, and possibly 10.8.3 as well.