I don't think that it's that people prefer the internet over actual books, but that people see the two mediums as fulfilling different roles. I think there's a difference between those who read on the internet vs. those who read books. For those who just want to find an answer to question or research something quickly, most people would probably much prefer using the internet. And even if their reading in the internet, it's still a different kind of reading, more like skimming, like the way you would skim through a textbook in order to fill an answer for your homework.
On the other hand, those who want to read for entertainment would probably prefer actual books. That's why most books are in the hundred pages length while online articles or stories are mostly meant to be read for a few minutes.