Well, that's what they tried to do. That was three weeks ago. The latest news (what this article is about) is that on their second or third try, the backed nearly all the way down, and are no longer doing that.
The reason I say "nearly" is that they're not trying to de-authorize the OGL 1.0a just for now; they haven't said they won't try to do it again in the future. (And, yes, I would agree with you, as does, for instance, Paizo, that that's not something they can do, and Paizo has said they will defend that in court.)
So, for now, WotC isn't trying to do anything that bad any more. They've gone back on trying to un-open all the gaming content that's been open for 23 years. Slashdot is a few weeks behind on this story. There's been a LOT of very heated response (and fairly one-sided anti-WotC response) on gaming message boards and th elike.