" Nearly $1 billion worth were sold last year, meaning 15 percent of all books sold these days are the kind that read themselves."
That seems... off. There were $15 billion trade sales in books last year (eg, not counting textbooks and the like), but audiobooks are massively more expensive than printed books. 15% of the dollars may be audiobooks, but each individual book takes up a lot more of that space.
Gang Leader for a day goes for $16 in paper, $25 in hardcover... and $34 on audio. But it can be even more extreme: Stephen King's Wolves of the Calla goes for ten bucks in paperback, $35 in hardcover... or $75 for CDs. Granted, all of these are list prices, and on Amazon (etc) may be lower. But even Amazon's discounted CD price is still $47, nearly five times the cost of the same book in paperback.
So while the rest of the article's perfectly reasonable, I remain very skeptical of the idea that audiobooks constitute 15% of the total books sold in America, even if they provide 15% of the dollars spent on books.