According to the study done by the NPD group, 58% of consumers who bought a netbook instead of a notebook were satisfied with their purchase. In comparison, 70% of people who set out to buy a netbook from the get-go were satisfied. This seems pretty straightforward to me: if you want to buy object A, but when you get home you see it's object B, you're going to be dissatisfied.
The study also dives into why people were dissatisfied, and this is where the cat comes out of the bag. As it turns out, people were expecting netbooks to deliver the same kind of performance and functionality as a normal notebook does. Consequently, they are dissatisfied when they discover that a netbook simply doesn't deliver. It seems like there's a marketing flaw here, or that salespeople aren't properly helping the people buying notebooks. Netbooks are for a specific type of use, and people who want a notebook won't be happy with a netbook.
Curiously, the ComputerWorld article also states that the costumer satisfaction figures are worse than those of normal notebooks. However, the article doesn't provide any further statements or figures for that, so where exactly it draws this comparison from remains a mystery.
Still, it wouldn't be too hard to explain. Contrary to popular belief, people are not snowflakes, and we all behave more or less in the same predictable and well-documented manners. A very well-documented behaviour pattern in mankind is that the more effort someone has put into obtaining something, the more likely he'll positively value that same something. If you spend 2000 EUR on a laptop and it sucks, you are less likely to complain about it than if you bought a 400 EUR laptop and it sucks just as much.
It's mostly related to the cognitive dissonance theory; the state of cognitive dissonance is more severe in the case of the sucking 2000 EUR laptop than it is in the case of the 400 EUR laptop. There are several ways to resolve a state of cognitive dissonance, but the stronger the dissonance, the less likely you are to solve it by accepting the new state (which would mean rejecting your choice for the 2000 EUR laptop as false). In other words, you're going to rationalise.
In any case, that's all just a guess. It's not at all unlikely that significantly more people dislike their netbooks than they do normal notebooks, but I'm not surprised by that if buyers have been mislead into believing that a netbook is the same as a notebook.