The difference being that Vista is a vastly superior operating system both technically and functionally, but was hindered by poor 3rd party driver support and relatively high (for the time) system requirements that were all but ignored by OEMs in the rush to slap a "Vista Compatible" sticker on everything.
Windows 8 on the other hand is a very incremental upgrade over 7 under the hood and will run on just about anything (same requirements as 7, which are the same as Vista), but offers little that is compelling to the average desktop/laptop user... unless you really like Metro, I guess.
Like I said, I'd happily upgrade to 8 if MS added an option to revert to classic/desktop mode with every trace of Metro disabled, but if I'm forced to deal with that, no thanks.