In reply to Will Hunt:
Do you know if those sales figures are specifically for climbing guidebooks or for books as a whole? If it's the former, I'd imagine that they're likely skewed by Rockfax*; if it's the latter, I guess I'm not that surprised because, because as you say it could just be a difference in between the perceived desires of the minority vs. the actual desires of the masses (i.e. most people don't really care, won't read this review, and are unlikely to give more than a moments thought to what's on the cover - let alone its texture!).
Still, it's funny how limited edition prints + hardbacks tend to get a nice matt finish, which then becomes gloss once it's available in paperback, so there must be some sense of value to it.
*it'd be interesting to know Alan's reasoning for using gloss as opposed to matt, as I'm sure this is something he's thought about