Sure, three months is a long time to fix an issue, but what does Microsoft have to gain by taking longer to fix an issue of this severity than it believes it needs to? If Microsoft released the fixes when they were going to, and Google then released the details of the issues and when they first reported them, Google could still make a stink about Microsoft's turn-around time on critical security bugs, and there wouldn't be any gap between global notification of the issues and a readily available fix for them.

Put another way, Google may have just notified the world of black-hat hackers of an issue they weren't otherwise aware of, an issue that demonstrably will not be patched for some time. If that is the case, then Google just recklessly endangered people's computers in the interest of raising awareness of Microsoft's poor turn around time on these issues. There is also the very real chance that this issue was already known by the black-hat community, in which case there isn't nearly as much lost by reporting here, but that's a gamble Google is making in order to make a point.

IIRC they do issue out-of-schedule patches if a vulnerability is severe enough and/or being actively exploited.