Hunting vs grazing
Reading is a largely passive activity, you pick up a book and the information is piped directly into your brain. Web searching is very different as rather than taking the information at face value, the expert data gatherer has learned that to track down the information they need, they must search for it from a variety of mixed quality sources and then interpret what they find to judge its usefulness.
This finding really shouldn't be a surprise. If we asked which would employ the most brain areas - reading Wayne Rooney's biography or going to your local library to make your own biography of Rooney - the answer would be clear. The inexperienced library user will probably just head to the biography section, but the experienced library user will include the newspaper microfiche, histories of Everton and Man United football clubs etc. Then they will have to compare all the sources to try and find what is true and what is false.
I'd say web searching probably mirrors human hunter gathering behaviour, perhaps specifically the type of data gathering techniques we employed when our day-to-day survival depended on knowing exactly what the other members of our social group were up to.