XP = DX9c. Vista = DX10. Vista SP1 = DX10.1. Vista SP2 = DX10.2. Win7 = DX11. WIn 7 SP1 = DX11.1. Win 8 = DX11.1. Win 8.1 = DX11.2. And now it looks like Win 8.1 SP1 = DX12. It really shouldn't be that difficult to grasp.
Perhaps it shouldn't, but considering that you got it wrong, as Microsoft added DX11 support to Vista, obviously it's slightly more difficult to grasp than you seem to think it is.