TS12 is based on TS2010 and previous builds, but with some tweaks and fixes (breaks).
Windows 8 is based on Windows 7 code which is a totally revamp from Vista.
http://www.microsoft.com/en-us/windows/enterprise/products-and-technologies/windows-8/default.aspx
Technically they both share the same legacy from Windows NT 3.51 if we want to go back that far.
But... In general, outside of the "modern" interface, Windows 8 is very much Windows 7 once you start using the desktop mode. What's interesting is with the new interface, you can bounce easily between the two forms very quickly with that start menu. I won't go into the details as this isn't the forum for it. What Windows 8 has though is some nicer utilities and things moved from the buried innards out to easier places to get them such as the top of the menu bar (ribbon) in the File Explorer.
John