There may be something to this. After years of following blogs, it can be difficult to bother putting in the time to follow badly written and complex stuff.
But by the same notion, when reading a book, I often find myself wishing for a chance to look up sources, find countering views, or write up a response--that is, I wish it was online. Books really contain a lot of space, and generally offer scores of smaller arguments. But you're probably not going to look up the references, and any individual argument is never exposed to the level of scrutiny given to, say, a single Krugman post, where hundreds of commenters will pounce, as well as other bloggers who link, and possibly replies. The evolutionary online system doesn't quite pare down the world of arguments into the best ones, but at least does a fairly good job of outlining the major fault lines and points of contention.
This balance is hard to replicate in book format. Take a recent read for instance, Maria Mishra's Vishnu's Crowded Temple. This is something of a cultural take on Indian history, which I found to be pretty interesting in general. But it displayed throughout a rather transparent ideological preference for a secular left-wing agenda against a perceived fascist alternative. For instance, Mishra implicitly blames slow growth under India's licence raj on "established buisiness interests" who captured policy; Her ideal solution would apparently be one more to the left. Hers is a common stance, but also a controversial one opposed by many economists.
Such debates online--say, at INI or Mint--involve a healthy back and forth, with competing data and arguments. With a book, you just get one side--in Mishra's case, a rather simplistic one. And even if you head online and look for reviews, you often get simple platitudes that don't assume reading knowledge. NYRB and LRB are of course exceptions, but often it's far easier to get a balanced view on a topic online rather than through reading.