I had Vista Ultimate, never installed, sold it for $200. I never got around to reading anything re upgrades to future Windows OS. So, indeed it's possible that M$ included that option (supressing my laughter). However, as Peerless said, it may also have been part of your deal with Best Buy. Gotta read the fine print.

I still don't know for sure if you need to clean install when upgrading from Vista to 7.