I've heard the same from those in the ski industry about things like AT boots. Economies of scale are a real thing, and there really aren't that many climbers/backcountry skiers out there compared to many hobbies (golf, fishing, water skiing, etc.).
It doesn't hurt that many weekend warriors have good jobs either. Non-dirtbag climbers tend toward white collar work, and companies often charge what the market will bear. Arc'teryx for example.
I would be interested to hear from a company like BD what proportion of their gross sales are through prodeals, and if they are taking a hit on any items. My understanding is that they are selling gear direct to climbers for the same price as they do to retail outlets. So I think that it is a bit of a stretch to say that their profits are being cut into by prodeals.
Retail outlets? Certainly. But the internet is a bitch, as Loren already pointed out with his recent purchases.