One thing I would say Rroff, is that the shadows thing is pretty noticeable, I remember all the way back to Bioshock, the only real difference between dx9/10 was the smoke, soft edges vs clipped edges is very noticeable. It used to be the smoke would look like a cloud with the corridoor(or whatever else) superimposed on top and so the clipping line where its just sitting "over" the smoke. But honestly I'll say I've not noticed it in many other games, maybe their dx9 smoke was just crap, who knows.
As for DX11, realistically theres VERY little a new API brings with it that CAN'T be done before, theres several things that were too complex with too big a performance hit to use without a new API but not really much thats impossible.
DX9/10/11, the main reason is to add improvements and simple make things easier, add short cuts, change rules that don't work and add ones that do.
At the moment due to consoles most people are still coding for DX9 from the ground up(well not quite dx9, but closer to dx9 than dx11) which means a lot of what we get now is tacked on. If it doesn't work under DX9 efficiently its not going in as especially for mainly console games theres little point spending a lot of time on effects that have to be disabled on your primary focus for release.
Tesselation is a hardware shortcut/aceleration of something VERY possible to do before hand. The memory usage and power drain of creating one of those tesselated uniengine images without tesselation would be immense though.