Apparently the water reflections at highest are really noticeable when you are flying.
I still haven't found any of these effects called tessellation though and I really don't see how they could be based on the screenshots.
This is the most thorough review of the d3d11 path I have seen. I've only skimmed it, but I see no mention of tessellation yet.
http://www.tomshardware.com/reviews/world-of-warcraft-cataclysm-directx-11-performance,2793.html
Warning: Ads after every click, very annoying.