"... don’t remember ever reading one of these books and feeling that I got substantial insights which were unavailable in the original article (in some cases it might have been useful to have a better sourced and slightly better fleshed out version of the original piece available somewhere, perhaps half the length again of the original piece, but there doesn’t appear to be a market for that)."
Wow. Does that ever resonate with me! I just paid $25+ for a 300+-page book that was an expansion of an article from The Atlantic. I did that for a Bloggingheads diavlog, and — you'll see when it's up — the author scolded me for skimming. Did that open the door for me to scold her for padding? Readers and writers — we all have our tactics and must guard our own interests. You pad. I skim. Or I take a look in the bookstore and put that thing right back on the pile. Unless I'm scheduled for a diavlog. In which case, I tough it out. Up to a point. Then I just scream. On my blog.