Well... A) Dissatisfaction with the system (Vista) probably rubs off on users' feelings about the hardware, and B) People go dumpster diving for cheaper and cheaper netbooks and other low-end junk - i.e. they're asking for trouble. If you sample Toyota customer satisfaction you're going to get one result for the group that bought a $12,000 Yaris and a completely different result for the group that bought the $64,000 Highlander. A brand that only sells high-end premium goods will have a higher average rating, obviously.
Those who buy $2000+ HPs, Lenovos, Dells etc are probably just as satisfied with those machines as they were with the $2000+ ones they bought 5 years ago.
It's not hard to find a quality PC... just check what a Mac costs, knock 20% off that and you have a good target price. If you buy one for half of what the Mac costs, you're on your own.
Yeah, the Mac's 3.36% marketshare worldwide is an indication that Microsoft will crumble to dust any minute now.