You never had directx 11. You have directx 10.1, unless you don't have Vista SP1 yet, in which case you have 10.0. 11 should be available with SP2, but you'd need to replace your video card in order to get the full benefit.
I saw 11 somewhere. Maybe it was while I was running Windows 7 as I have a dual boot system.
In Vista64, i ran system restore and ran it back to 'before updating direct x" and now I have version 10 as you say. I didn't look at the exact version but you are probably right, it's 10.1. I'll check next time I'm back on the desktop pc - using my notebook right now.