It's not stated specifically in the article, but from the large number of respondents who offer act as both designer and developer, I suspect this survey is focused on web freelancers, as opposed to developers in general. I would expect to be able to charge far less for generic CMS-backed web site building than for more specialist areas.
Agree, I think there's a proportion of freelancers who do a mixture of boilerplate CMS development and backend development who have very different day rates for each just because the going rate for each is so different. It would be interesting to see the fraq.info web app expanded to include and use data from an ongoing survey which distinguishes between types of development.
