Oh really? Looks like I have been misinformed.... But Wasn't 7 built off Vista?
Of course 7 (NT 6.1) was a later version of Vista (6.0). Vista was a later version of XP (5.1). XP was a later version of 2000(5.0), 2000 was a later version of NT4, etc.
But that's the thing. Ubuntu 10.04 isn't regarded as a distro of Ubuntu 9.04, just because it's a later version. Ubuntu, Slackware, Fedora, Mepis, KUbuntu, Mint, etc are Distributions of Linux. They aren't different Versions of Linux insomuch as they are completely different Operating Systems based on Linux.