He has a point, but I don't think it's a good one. He might have a better one if he gave examples of Ballmer's ethical behavior.
Yes, the GPL has some coercive aspects to it. But it's right out there in the open and has been since v1. You don't have to worry about Stallman changing the terms once you've committed your business or livelyhood to his tools. You do with Ballmer.
In situations like this, it's often useful to "follow the money". Ballmer and Gates are clearly after power and riches. Stallman isn't. Ballmer and Gates want control of your data and code. Stallman wants to prevent others from controlling your data and code. Using that metric, Tim's wrong.
My $0.02.
Cheers,
Scott.