At current Microsoft anti-spyware is a repackaged application they purchased elsewhere.
It's provided as-is while Microsoft is working to update and enhance it.

If it doesn't remove some things, blame the original developers rather than Microsoft...

Of course many anti spyware tools (especially free versions) tend to have a lot of false positives in order to scare people into spending money on the full product.
As Microsoft AFAIK has no intention of making money out of their product, they don't have a need for such shady tactics.