@fanbaby: Part of the problem (in my experience) is quality control -- taking a 'jewel' from someone you don't know might well turn out to be made of paste, or even worse contain arsenic that poisons everything.
At least if a big company releases something open you can have a higher level of confidence that the quality will be good without having to spend the time performing your own quality control.
Additionally, larger companies tend not to use the latest GPL which I have come to dislike for being too dictatorial (and therefore less 'free', ironically).
I've rarely had a problem with the quality of an OSS product; the issue is usually that the project gets abandoned.
But this can happen with commercial software, so ...
With someone like Microsoft running this, you can guarantee that the whole shooting match will be well documented, something that OS often lacks.