I mean, I could argue that people shouldn't work around iOS bugs and should instead apply for jobs at Apple and fix UIKit itself so that everyone can best benefit from their labor. But that's absolutely absurd. It's also more than a little unfair to judge members of the jquery team for not going into a project like WebKit that's millions of lines of C++ and acting like they're coming up with excuses for "not fixing bugs". This is a symbiotic and healthy relationship, browser vendors benefit from groups like jquery that make those bugs livable today through workarounds so that their products can be more usable in the immediate and they can focus on the "real" fixes for the future.
And don't forget that there are people who are running old OSes that would require buying a new computer before being able to upgrade their browser.
2. Even if it were to make it into a shipping browser quickly, there is no guarantee any reasonable amount of people will run that upgrade anytime soon.
Hitting browser bugs really sucks for this reason. The bug has to be worked around no matter what, since there will probably be people running that bug for a long time (this has gotten much better with things like Chrome's auto-update which is why if you talk to people from that team they are such big believers in it). Regardless, you have to remember that the jquery team is providing a product to clients. If a client's site is broken because jquery hits a bug in a browser, the priority is to have that site work asap. Its unacceptable to say "Oh we fixed the bug in webkit, Safari users will see it whenever the new Safari ships which we have no idea when that is since its an apple secret. Bug closed." The best response is "Fixed in new jquery version whatever, just update the script on your site". And once you've fixed the bug for your own concerns, it just doesn't make sense to then spend time fixing it in WebKit as well vs. spending those resources on fixing another jquery bug.