or just getting rid of shares before a collapse of confidence in the company?

Comcast is one of the best-placed cable operators in the US. It's stock hasn't 'tumbled': it HAS fallen by 15 percent, but that's far less than most of it's competitors.

Microsoft sold these shares simply to cover their own losses - notably in online, Xbox and entertainment - and also in order to raise funds for the failed bid for Yahoo! Microsoft sacrificed a very valuable asset, and this decision (made at the height of the financial folly of last year) is simply another reflection of the inept management currently residing in redmond. 9 billion, they have, now - partly based on market value, which can change, of course. Remember when they had 45 billion? Around about 30-40 billion has bled out of that company, over just the last few years: now THAT's a story.

Maybe it has to do with this:

http://www.theregister.co.uk/2009/01/21/fcc_letter_comcast_voip_traffic_management/

In any case, the fiddling Comcast has recently been doing with their customers' bandwidth could turn a lot of them away (it would turn me away if I was one of their customers).