OGL offers little extra compared to DX10.
The OGL consortium know they took far too long to get this standard out, and as a result it's behind the curve.
Plus M$ can just give developers large wads of cash to stay with DX10.
it has one trump card... windows XP (and to a lesser extent linux). DX10 requires vista... infact if it wasn't for this fact open GL3.0 would probably not exist, its only really due to developers looking to support the newer hardware features on older OS to broaden their market appeal thats really kept any life in it at all.