Features as large as multi threading a part of the bge cant be tested by the dev for every single use case, especially with animations there’s so many ways they can be used with types of objects.
If I remember correctly this did have a branch separate from master with which it was worked on, but what blender user let alone the majority of very young bge users would have been able to find that branch let alone build it and test it. So adding to master when its working and stable to the dev which im sure it was before the merge is the only way of getting it into a larger user base for testing.
Then that leaves the bge users that one read the tracker about stuff added for the bge and then knowing about build-bot to test with then even bothering to report the bug as many of the bug reports for the bge are consisting of one line of text and not even a blend to recreate the bug with.
I reported a few bugs for animations early on in the 2.71 cycle which got fixed, Other reports came in after release candidate 2 for 2.71 very close to release, showing that people don’t test until an rc build is put up onto blenders main page or with a final. But this isn’t something just akin to the bge, people do this with blender bugs in general which is why we have a and b versions after finals.
So this isn’t really good enough if you want bugs fixed in the bge that have no work around for crashes, make sure to get reports in early when you find them. Showstoppers in the bge will not halt a blender release sadly.