George Ou asks Why can't Microsoft just patch everything?, in response to the recent known-bug exploit. There are obviously some good answers to this question, the most likely being that a new patch is likely to introduce new bugs, and ugly legacy code is hard to patch. However, Microsoft really does have the resources to tackle this if they wanted to.
I guess people just need to remember Microsoft is a shove-it-out-the-door programming outfit run as a marketing/sales company. (Unlike google which is a shove-it-out-the-door programming outfit run as a elite-programmers company). Patching and security just isn't very microsoft, its going to take a while for them to adjust.