Microsoft's being stupid. WebGL is a way to write 3D on the Web, something that's so far not been possible. All the Direct2D stuff is orthogonal -- you can accelerate 2D drawing and provide 3D support separately, as Firefox does.
I wouldn't be surprised if they released IE with DirectWeb or WebX, or something ;)
That's all there is to this story. WebGL competes with Silverlight, and real-world WebGL adoption isn't very high yet. Microsoft therefore feel they stand a chance.