The data comes from ChangeWave research, which might not be as comprehensive as that from the University of Michigan's American Customer Satisfaction Index, but it does focus on "senior technology and business executives in leading companies of select industries", which implies a ore demanding sample group.
In any case, the figures are pretty clear. Among customers who purchased a Mac over the past 90 days, 81% say they are "very satisfied", followed by 67% for ASUS, and 61% for Acer (both with a strong netbook presence). Dell scores 55%, and Lenovo 50%. The report has other interesting data, but I want to focus on customer satisfaction for a moment.
Customer satisfaction is a very difficult and complicated concept, determined by so many factors that it's hard to explain properly. Contrary to popular belief, being a satisfied customer does not mean "high quality". More accurately, it signifies to what extent a product has fulfilled the expectations of said customer.
Let's break out the car analogies. People who spend 50000 EUR on an Alfa 159 will have different expectations than people spending the same amount of money on an Audi A4. Alfa Romeo owners will accept more failures and breakage form their 159 than Audi buyers will tolerate from their A4. The reason for this is differences in expectations: an Audi doesn't break. With an Alfa, it's part of the charm (even though it's not nearly as bad anymore as it used to be).
What this means is that similar products at the same price points will be treated differently, leading to a different sense of customer satisfaction. Said Audi showing minor defects within the first 10000km will lead to a bigger blow to customer satisfaction than that Alfa doing so. And that's just one of the many factors.
In the end though, the goal of a company is to make a product that satisfies customers. As has been shown time and again, Apple does a good job of doing so, and it turns out that Acer and ASUS are good at it too.