A mere 20% spread? Ha!
Looks to me like the average consumer doesn't understand what good and bad service are. Perhaps because they've not used more than one broadband provider, and assume that they have a typical experience — be it good or bad.
I've personally had service from three of these companies, as well as knowing of others' experiences with them. The approximately 10% spread across my current provider and the others does not do justice to the black-and-white nature of the difference.