Imagined reasons ? I wanted to know why they were asking as they didn't say beyond querying whether it would run on older systems. Installing 7 would provide little in the way of additional functionality to a casual user and if it's speed then a cleanup of the computer with say ccleaner or a complete reinstall of vista or more memory might achieve the same thing.
A fresh install would certainly do the trick and more memory for vista in a lot of cases. However people don't actually necessarily behave like this in the real world. People don't bother reinstalling and often justify what is 'effectively' a reinstall by buying a new OS. I would hope that people understood that I'm not advocating paying 'full price' for windows 7 (or 8 for that matter) for the sake of it. However £30 for a quality of life improvement I'd say is as good a reason as any for going along with this madness. Or they could buy an SSD. And so on.
Vista was crap (in the sense that people said so at the time). That's not picking on vista, a very similar thing happened to XP, it's just again like vista people had it for such a long time that it worked out in the end due to faster machines, very major service pack updates and various other issues. It's just that over time revisionist history came in and XP was seen as the best ever OS
written on stone tablets and all that twoddle. Vista is now suffering from the same kind of revisionism.
The feel of 8 is very different and leads some people cold, but that's exactly what people were saying about Vista.