I dont think DX10 even today has much popularity... yes some games have it but from what I can see its 40/60... with 60% of games still being DX9 only.
Win7 will help DX10/10.1 A LOT and I'm sure more and more games will adopt this new technology because there will be more users switching from XP in the next year.
I dont think DX11 will be widly implemented until 2011+.
Another thing hindering DX10+ development is "consoles"... since they are DX9 only... lazy developers who only port games are not making a DX10 code path.
A shocking example would be the new "Call of Juarez : Bound in Blood". This was one of the early (or first?) DX10 games and the sequel (or prequel!) is actually only DX9... only because the developers main focus is consoles and a ported PC version. Sadly.