tx7321 said:
1E is God...

Diaglo would disagree. Merric: "I know AD&D (1e) certainly had a time when it was the "hot new thing".
Craze is a much better word than fad in this context; thanks. I was looking for such a word, and just couldn't think of it. (No edition of D&D is released as a "fad").
We didn't see the "gotta have this new product" model going on. What we saw were new modules (with pretty conservative covers), Dragon, and smaller supplements.
Actually, we didn't see smaller supplements (as such). Mostly new modules and Dragon magazine - Dragon was the only place for new rules material, which is probably one reason it was so popular during that time.
3E puts out alot of material that does effect the core. A trip to the gaming store this last weekend overloaded the senses. I could barely find the C&C material I was looking for. They flood the market with new supplements.
If it were merely a fad, there wouldn't be so many supplements overloading your senses, as the lifespan would be shorter.

Wizards produce about 2 books a month, which while a lot from an AD&D perspective, isn't really that much (certainly not from a 2E perspective!)
That said, WOTC set up 3E to create a cash flow through constant release of new supplements that effect the core game (not just adventures, monsters, magic etc.) so its "gotta have that new prestige class, new feat etc." so is, in a way, Fadish (by the definition I posted to PirateCat).
Wizards do get revenue from constantly releasing new material. I wonder if this is a gamer thing (most profits are in the first 2 months) or a phenonomen with everything - I suspect the latter.
I think early on TSR hoped AD&D would be one feather in a cap of many FRPG games like it; but the economics of publishing required its flagship to continously change to sell new books (so instead of being a stable system like Monopoly, it had to drastically change every few years). When 1E first came on the scene I think the dynamics of the market weren't really that understood. Also, I don't think the company really expected to grow the way it did. Once the engine was their it needed more fuel then ever to keep it running. It wasn't any longer a few guys in a basement, it was something much bigger.
D&D has a big difference from the book market: the D&D core books aren't really consumables. With most book buyers, they get the book, read it, and then put it away and buy another book. With D&D, they get the core game, play it, then play it again, and again, and again...
What distinguishes D&D from other games even more is the time investment required. If you play D&D anything like most people, you play it in a campaign that takes 4 hours per session, and many, many sessions! That's quite different to other games, where play is discreet, and not ongoing.
The closest we have in the present age is
World of Warcraft, and that, of course, derives from D&D. Where WoW is better is the subscription fee, so the makers can keep making money from the game! No such luck with D&D!
With a boardgame, you can own several games because to play one doesn't exclude you from playing another on the same day or the next day. (So says the gamer who's bought 15+ boardgames in the past year or so...) Meanwhile, the D&D player has a game, and then wants to return to another D&D game. Although play of Top Secret or Star Frontiers could be possible, the RPG structure works against it, if simply for the effort needed to learn the game (both as a player and especially as a DM).
I think it was about 1983 that TSR really lost Gygax as a guiding force, as he was sidelined before he left in 1985... so, Gygax was there during the initial growth period of D&D. We never really got to see him
sustaining the game, which needs a different strategy, of course.
As an aside, post-1983, I don't see any real classic adventures. The latter Gygaxian efforts (Dungeonland, Isle of the Ape) are a bit too whimsical, IMO. And T1-4 was... disappointing.
As Gary noted,
Unearthed Arcana was created to build revenue quickly, and it did so. That it also set the pattern for 3e releases is not unnoted: players like new rules material!
Cheers!