Depends probably what games you looked at. If these were not optimized for DX10, you won't see much of a difference of course.
DX 10 brought pretty impressive optical improvements in terms of water (water surface ripples, waves etc looking way more realistic, fountains, under water effects etc.), the ground cover in games looked much more realistic, especially its lighting and fade-in of spots with ground cover. Distance blur inproved, softer shadows, polygonal round shapes becomes truly round.
Might not be much for you but it matters a lot if you play for example a MMO for years and re-visiting the same area quite some.
DX11 brought better surface plasticity without modeling it. See here: http://www.youtube.com/watch?v=wtNHmj7vznI Not sure otherwise, I haven't seen anything in games yet that fully uses DX11 functionality.
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