There is no need for dx11.
Tesselation make it able to change the number of polygons of a mesh on the fly,based on an option to use more complex meshes,which means more polygons.
But someone could just create one very complex mesh from the beggining and add it to the dx9 version of a game.
yeah.... except that with hardware tessellated object will use a fraction of the mem bandwidth as a presubdivided mesh. Something like a 1k tris going through the card as opposed to something with 3 subd levels making it 64k tri.(which is actually currently the upper limit to a single mesh object in OB/F3 lol) also as I understand it, you can store vertex data, like skinning or perhaps UVs, colors? dunno, in the vertex shader, before the tessellation shader comes on, you just try running skeletal animation on a rigged mesh with 100k tri and see if that actually even works in any engine and rig... but this works in real time with hardware tessellation though.
What you have said about actually using dense meshes to begin with is not equal in terms of performance. by a long way! this is whole reason hardware tessellation exists. You simply cannot equal the geom level on screen of tessellation, just by firing as many polies on screen as possible. one scene will be max a few million, the next would be an order of magnitude greater in geom.
plus LOD system with hardware tessellation is easily the best solution- on one hand you create 1 mesh and the shader does the rest without having to fetch and reload new geo, on the other you create up 3/4 versions of the same object and the engine will do a swap and replace with a new higher rez version of the object as it moves closer in the zbuffer. which means you only need 1 low poly object and the displacement and tessellation can do the rest, instead of having to pack several of the same mesh, all of which bar the lowest would be increasingly larger in file size something like 100kb as opposed to, 100kb+250kb+500kb for the LOD versions. DX11 Disk space win.
anyway yeah... DX11 shaders are pretty rad. but while cool, i am agreeing with anyone who really doesn't care very much if it happens on the pc version. I doubt they would do anything amazing with DX11 anyway. to really use it well, you kinda have to go at it with teeth bare and say gimmie that good stuff. I suppose some shaders would look a little better if they tack it on at the end. I'm not making the mistake, they would be trumpeting if they were the least bit excited about using it... which they haven't. so I doubt it. and if they do use some of it, it'll just be a marketing ploy for adoring fans.