Direct3D seems to be unstable API. Excute buffer no longer supports new hardware features. Same for Retained mode. To take advantage of new hardware features, people often have to rewrite large part of Direct3D codes.

I heard that OpenGL code need not to be re-written to take advantage of new hardware features. Why do I need to rewrite Direct3D codes?

Well, I don't think it's that huge of a deal. Few people actually use Execute Buffers and Retained Mode. True, you do have to use new interfaces to take advantage of new hardware, but usually it only takes about a day or two to update if you've been keeping up.

One thing you must remember is that It's a bit unfair to compare OpenGL and Direct3D in that manner because OpenGL has been around for a lot longer, and most of the "new" features in OpenGL have actually been in for quite a while on high end workstations.

--TheGoop