Rjstreet over at Purple Pawn has a great article analyzing Games Workshop's financial performance. That got me thinking about the nature of the business model of the role-playing game industry. Games Workshop has a model that presupposes that their customers will continue to buy new WH40K figures, on the assumption that new figures (and, by extension, new armies) allow the game to be played in new ways, preventing the game from becoming stale.
RPGs seem to have a related sort of business model, but not quite to the same extent. Where WH40K has new armies and unit types to add to diversity and new options for game play, RPGs must rely on either rules expansions or pre-written adventures to keep their customers coming back and forking over that credit card.
But I would argue that the situation from the RPG side is much more precarious than that of the miniature game company. Once the "core rules" have been purchased, regardless of the game system, the customer is no longer beholden on the company to provide expansion material. Unlike their WH40K-playing cousins, who are hard-pressed to make their own models and cast their own molds, RPGers can write their own expansion material if they so choose. They don't need to buy the latest Monster Manual if they don't really want to; they can write their own stats for Lolth or the mimic. The experience towards the end of D&D 3E, with a gazillion and three "splat books", most of which are still to be found in bargain boxes in game stores across the country, demonstrates just how replacable such things are. Adventure modules are even more problematic; most RPG rules are written specifically to allow (and in many cases help) the game master to write his own adventures.
I'm inclined to think that there is no commodity that the RPG publisher could come out with that the customers would have more of an incentive to buy on a regular basis, other than the rules themselves and the occasional major rules supplement. Something that would increase the options for play, but that are of such a nature that they would be superior to do-it-yourself. WotC has tried with their own lines of miniature figures, and tilting the rules of D&D 4E to almost requiring figures, but they didn't overcome the problem that many gamers already had boxes and boxes of figures, and the newer ones didn't really add anything, other than having 4E on the box. Their battlemats are closer to what GW is able to do, but even there, Photoshop seems to be digging into their profits more than piracy ever could, since gamers are able to create their own gorgeous customized mats for pennies.