It's really up in the air whether AMD tweaked the 4000 series tessellation engine for DirectX 11 or they didn't have to do a thing and DirectX 11 merely required having one.
So let me back up since I may be confusing myself and you. DirectX has a list of hardware specifications that the manufacturer must meet in order to be DirectX complaint. As far as I can gather between major versions:
- DirectX 6 wasn't any thing fancy other than optimizations for CPU instructions (x87, MMX, 3DNow!) and texture format support
- DirectX 7 required transform and lighting on the hardware itself.
- DirectX 8 required the hardware to allow for programmable vertex and pixel shaders.
- DirectX 9 was weird, but the hardware had to support high level shader languages, multiple render targets (a requirement for deferred shading), and floating point texture formats (required for HDR rendering). 9.0a was optimized for NVIDIA's implementation for 16-bit floating point textures. 9.0b was more for ATI and their 24-bit implementation (although DirectX 9 required 24-bit floating point in the first place...). 9.0c just tweaked with the parameters on shaders.
- DirectX 10 required a geometry shader as well as unified resource allocation. I suppose in light of this, hardware manufacturers took the route they did, instead of what AMD did with the Xbox 360 GPU (which superficially looks like an X1800, just with a unified pipeline). Wikipedia says there's also "Instancing 2.0", which suggests that DirectX 9 had it.
- DirectX 11 required a tessellator and support for compute shading.