I'm actually a big fan of several Microsoft products, and think their stand on WebGL is completely right.
OEM video card drivers have a history of already being unstable. In all likelihood, this represents an attack vector that, up until this point, I hadn't even thought of.
That said, it highlights something that has become somewhat of a trend with Microsoft. They seem to have decision making in almost every area being done by different teams who don't talk to one another. While I agree that OpenGL isn't "safe", what about ActiveX? Isn't allowing a browser to execute arbitrary code directly against the processor (regardless of whether or not its "signed" and the user had to click a few dialogs), a far greater threat? I'd love to see a press release that indicated they were ripping that functionality out of all currently supported browsers. What about Silverlight? I thought that had elements of hardware acceleration (perhaps it's protected enough, who knows?).
Kudos, to them, for taking a well reasoned stand for security in an application type that is routinely used to attack users, but I'd like to see the other 'harmful' features addressed as well. For now, I find Firefox with NoScript and Adblock+ to be the safest bet.