Quoting from the Wolfire Games Blog:
"The tesselation technology that Microsoft is heavily promoting for DirectX 11 has been an OpenGL extension for three years. It has even been possible for years before that, using fast instancing and vertex-texture-fetch"

Well, huge amount of details, but, as the recent "realistic" 3D we see in games, I still find it ugly (not on the artistic part, as the post says that the 3D has been made by techs and not artists) and unrealistic.
It seems that, as we can see it in UT3 or Crysis, the devs think that they have to put the most possible amount of bumps to make 3D look realistic, but it's just ugly imo.
In fact, it looks like pre-calculated 3D we saw 10/15 years ago.
This 3D era we're actually in will get old very fastly imo.

That is a vendor extension from what I know and can stop being supported at any moment if they decide it has to be deprecated and a wrapper isn't written for it.
It also heavily depends on how hard to use is a given API and most seem to ignore the fact that:
a) DirectX is easy to use and has an excellent documentation and most importantly support
b) DirectX isn't just a graphics API (Direct3D) but also sound and controller so it does much more than OpenGL.
Also, please take that article with a grain of salt as some of the things said there are absolutely false.

If you refer to the comments on that blog post you will discover that it has many, many inaccuracies, including how long the tesselation extension has actually been available. Despite this the author has not corrected his post.
Anyway, what really matters is that OpenGL tesselation only works on a tiny portion of systems, and ATI will be dropping support for it in the near future in favour of compute shaders. DX11's tesselation, meanwhile, is vendor-independent; since it is part of the official specification--not an extension--and runs on the multi-purpose compute shaders (which can handle various GPGPU tasks, not just tesselation) it will be supported by any and all future cards, even once DirectX 12 or later is released. Nvidia-only hardware PhysX utterly failed (most games use the CPU-only version), and some-ATI-only tesselation would fail too (that is, if Windows developers actually cared about OpenGL any more--which they don't).