I think computing for a lot of people has become an appliance, or close to it, akin to their refrigerator, dishwasher, or even their TVs. You turn them on, use them for a bit, and then shut down/sleep and forget it. They don't want to think about things like maintenance, what's new "under the hood", etc - they want to do what they always do (whether that be run the same apps, check mail, browse the web, etc), and move on with their lives.
I too have become one of those people over time, although I still find new tech interesting. However, Win7 was sort of a change in this regard - it gets up quickly, gets out of your way, and does things in a more "human" manner than previous versions of Windows used to (in fact, with the superbar, it's even more designed for folks to use by muscle memory than XP ever was). I treat my PC now the way I have always treated others PCs that come to me for help - you set it up initially, properly; install a good anti-malware bundle that will stay updated automatically (MSE is perfect for this), and enable automatic disk defrag (which is helpfully done for you out of the box). The PC then becomes, basically, an appliance that self-maintains and is easy to use.
I have to agree with the statements that most folks who don't upgrade right now are probably just happy with the status quo and will worry about a new OS when they get new hardware, but we'll see the same sort of zealotry in a few years that you generally see from folks in the Win9x scene today, or the folks that are sticking with Win2K are starting to become - they'll cling to an old OS like XP with everything they've got, and everything else ever made will be "crap". Technology will pass them by, but for the vast majority of the long-term holdouts, it probably won't affect them much at all until they can't find an XP installation disc or ISO anymore