The headline is a bit weird. The article is about “these apps are so popular, Apple went out of their way to ensure they still worked”. It’s not clear that the apps were buggy, except in the NSBundle unload case.
To me it’s more accurate to say that Apple frameworks are buggy and older versions of those apps had to use workarounds and depend on the buggy behaviour until Apple decides to fix those bugs.
I wouldn’t be surprised if Apple knew about some of the bugs from the developers of the apps during the beta period of a new OS. It doesn’t necessarily mean that Apple actively tests all of those apps as part of its OS QA routine.
Yeah to me the article read like “Apple consider’s these apps important enough that they go to extra lengths to ensure OS updates don’t break them”. The title here seems weirdly judgey and negative.