Yeah, publishers still have to pay people to be editors and writers.
With books/magazines/journals/etc you are reading something from someone who is almost always being paid, and companies that want to stay in business do not pay people who are idiots.
By contrast, any fool can publish stuff on the Internet - and they do!!! 
There is lots of great free content on the Internet, but it often lacks the rigor and editing for which published materials are known.
P.S. There is this publisher called SitePoint that puts out some pretty nice books - which I have bought - that can compete with anything on the Internet. (I enjoyed some of the SP CSS books…) 