Part of the reason why it's hard to fix bugs that people have worked around is because the fix often breaks the workarounds. Which causes a problem for Apple either way; either they can leave the bug in and let everyone work around it, or they can fix the bug and break all of the myriad apps that use the workaround. Depending on the circumstances, they can actually put workarounds into the frameworks to preserve bugs for apps linked against older versions of the SDK or for apps with specific bundle IDs, but not every fix is amenable to that kind of solution.
Which is to say, there's a good argument for the idea that reducing the ability to monkey-patch framework classes will make it much easier to actually fix bugs in the frameworks.
>Part of the reason why it's hard to fix bugs that people have worked around is because the fix often breaks the workarounds.
That was a problem for Microsoft, Apple, from all we publicly know from their releases, never treated that as a problem. They went ahead with the fixes even if it broke previous workarounds.
Which is to say, there's a good argument for the idea that reducing the ability to monkey-patch framework classes will make it much easier to actually fix bugs in the frameworks.