(in reply to some other post, not quoting since the forum screws up my posts anyway and its a pain to fix every time)
I don't quite see where the info that microsoft purposely slowed down OpenGL for Vista came from, i was under the impression that the OpenGL->D3D wrapper they added in Vista only were supposed to replace the insanely slow OpenGL software renderer they had in older Windows versions. (So if anything they made OpenGL without proper drivers faster)
There was (and I'm working on memory here I admit) a couple of aspects to it one of which was real with regards to how OpenGL frame buffers would compose with the D3D driven desktop and windows however that one did get sorted out once MS gave a little on it with some pressure from the IHVs.
The other is, as you say, regarding the apparent OpenGL->D3D layering which many took to mean (without bothering to look into it, just looking at a slide) that OpenGL would sit on D3D; what it REALLY meant was MS was going/planning to provide a OGL1.4 implementation based on D3D (I'm not sure they ever did in the end at that.)
(At the time this was going down I was using OpenGL, I heard the above did a 'ffs...' and then once I looked at the details realised the panic was rubbish in this regard...)
With regards to MS 'slowing down' OpenGL; many many years ago they were on the ARB (pre-2003 I think?) so they had opportunity to do so with regards to the spec but they didn't have to. Back when the ARB was an infighting mess, a running conflict between the interests of ATi, NVidia, Intel, SGI & 3DLabs so getting anything done was a nightmare which is why nothing got done - GL2.0 was the first causality in that war and Longs Peak was the most recent even after they all started to get along..