On the Web, alternative reading to whatever you're looking at is never far away. There are even links in most Web pages, forever calling you to random-walk. The result, for the reader, can be a haphazard adventure of reading, interesting at every point but without overall purpose.
The result for writers is that time spent organizing thoughts is usually wasted—nobody wants to read all that. Instead, you write one thought per day in a blog, or contribute to sites like Wikipedia, which generally rejoice in the Web's random-walk nature.
Sometimes it is an unexpected pleasure to open a book and follow the development of a big idea over many chapters. I got this kind of feeling from the mathematics textbooks I mentioned a few days ago.
It's weird for me to even be saying this, because I like that the Web is deeply interconnected and wild. But the Web doesn't seem to generate good content with large-scale structure—the kind of stuff that I find most rewarding to read.