I teach Computers to grades 6-9 and I have noticed they have a hard time "reading from a screen".
I do a whole unit on skimming and scanning for reading comprehension when I teach them to identify high quality sites, BUT they need more practice. Unfortunately we do not have a whole lot of other computers for teachers to help kids when researching, so most of their "reading" when selecting sources is done at home and with little or no help.
The kids at school do read a lot of books. This, in my mind, is very linear and simple when compared to the layout of content on a website. So reading books doesn't seem to provide kids with the practice they need.
What do you think about magazines and newspapers? The layout is in columns, with a huge varierty of fonts and sizes. Colourful ads distracting from text, and a whole lot of pages meant to be skimmed and scan in a short period of time.