Robert Scoble on why Ballmer isn't believed:

My friends have been asking me "why doesn't Wall Street believe Steve Ballmer?"

That's an easy one. Cause he didn't convince the grass roots influence networks first. Why have Google and Apple done so well in the last three years? Cause the grassroots loves them. That's the powerroot of the industry. Ideas here don't come from the big influencers and move down. No, they start on the street and move up. Anyone miss how Google got big? Not by throwing a press conference.

I have a far better answer, and it has to do with the track record of delivery. How many revs of OS X has Apple pushed since Windows XP shipped? Meanwhile, how many revs of Windows has Microsoft pushed? This isn't about influencers and grassroots - it's about actual delivery of real products - something Apple excels at. Microsoft? Not so much.