Perhaps the bigger question about the Exchange bug, is what changed between versions? One way you get to a stable Application is by making good use of modular code, and having a robust API structure, internally and externally.
This exchange bug appears to be in the core calendar application, specifically when handling calendar meeting requests and updates (something that has never really worked well, but lets not get started on that with Apple and Exchange). What did they really need to change about this functionality between iOS 5 and 6? Communications should logically be handled by a different module, display as well. I can't think of a very good reason they would need to change anything about the handling of this if it was working from the prior release. That doesn't mean they didn't need to.
These bugs just make me question how Apple is actually designing this system. Most mature software is a fusion of very old code - stable and tested that has been there since the beginning of the Application (or even from something else!) - and new code and new modules that either completely replaced most interface and logic functions. If iOS is to be considered stable and mature (and at version 6 I should hope it's approaching that), then bugs like this make me wonder just what they are changing and how well they modularized various functions in the first place. I have a hard time thinking that their exchange calendaring code has changed that much since, what, iOS4?
Perhaps it's time for Apple to make all of if's "built in" apps, actual apps, or at least treat them as such. At the very least it would force them to creat a standard API interface - even if it wasn't exposed for other developers - as well as enable them to issue updates only for the apps in question.