It has nothing to do with worry, and everything to do with investors.
It has everything to do with worry. Have you seen the numbers on college campuses? Sure baby boomers like their PCs, but Gen X and Yers are choosing Macs at eery opportunity. The decisions made in college are going to be lifelong lifestyle choices and MS doesn't find a way to curb it, the next generation is going to raise their kids on Mac. The only way MS stays in this is corporate IT, but those jobs are getting handed down too and eventually someone is going to say in a meeting, "We spend so much money on IT and computer repair, what would the long term savings be to go Mac?"