Everybody knows that the computer world moves really fast. Technologies update quickly, prices drop quickly, and young upstarts like Google can easily take on old farts like Microsoft. When you move into open-source and Ubuntu, things move even quicker (sometimes). Ubuntu has a release schedule of 6 months at the most, compare this to Microsoft which as of late is 5 years and in their earlier days, 2-3 years; or Mac OS X, which is usually about 1-2 years.
While it's nice that updates come so quickly, they do not do so much to get rid of the impressions the older bugs make. From my experience, when people try out a new software and it doesn't work or there is something wrong with it, they will assume that the problem will stay there for a long time. If there was a bug with Gutsy when it came out, chances are the people still using Feisty are using it because they think that the bug with Gutsy is still there. I'll note that Gutsy did seem to have a lot more bugs on release than the other versions of Ubuntu that I've used (Edgy, Feisty) but most of the ones I've seen have been cleared up by now.