From what I can see, it's not trust - it's ease of use. People are used to MS - what do they see everytime they switch on their pc? When they go to Start to open a program? When they surf the Internet?
As far as Joe Bloggs is concerned, Microsoft is trusted - try run his pc, and by default everything on it.
On a side note, once MS start unveiling their technology, would Google / Yahoo! actually have the resources to keep up the arms race? If they get into a feature race, then who has all the best research labs out there?