Wow. What a ruccus I've stirred up!
I'm sorry to have given the impression of disrespecting any particular d20 publisher. Let me make clear that my comments were quite generalized (please note that I said "most" companies this and "many" companies that). Obviously there are companies that still make adventures, and obviously some companies that have abandoned them make other products that are quite good and serve a valuable niche in the portfolio of game products available to the d20 gamer. Where those things are true, my comments obviously don't apply.
But here's the thing (and this also speaks to my comment about WotC making the best hardcover supplements): We have a distinct and unsurmountable competitive advantage in the category of core supplements. We have the highest production values, and the economy of scale to carry them out in every single product. We have core designers who know the game better than anyone--and not just the game as you see it on the shelves now, but also as it's evolving in products that won't be out for another six months or a year. We have the most powerful brand in gaming--perhaps in fantasy overall. And we have the largest, most experienced collection of game-design minds assembled on this planet. The tastes of any individual on these boards notwithstanding, for these reasons we will alway dominate the market for hardcover core d20 supplements. [Oh yeah, and we're just darn good. Of course I believe that--if I didn't, I'd go work for someone else!] Anyone who wants to scoot up to this buffet, as someone analogized, is going to have to do something truly unique, or they'll find themselves clawing over our scraps.
Compare that to a typical adventure: A creative, talented author with a good idea, a solid grasp of D&D, and a few thousand bucks can put out a really good adventure--perhaps as good or better than anything we can do. Aside from our brand, all of our competitive advantage is neutralized in this category.
My hat is off to those companies that have made unique product lines and found a place for themselves. But for every one of them, there are twenty that didn't. (Remember, from where I sit, I see the entire d20 spectrum--not just the companies that do well enough to develop a vocal following on EN World.) Those twenty have choked the RPG supply chain with product that doesn't move because it doesn't address a need or do anything better than what we do.
The key to a healthy gaming marketplace is a diversified portfolio--a range of products offered to the consumer that cover all of his or her needs, with just enough duplication to ensure healthy competition. The d20 community, as a whole, hasn't delivered. (And again, this isn't a slam on any company that is delivering!) That results in A) a hole that WotC is now going to fill, and B) a d20 industry that's really struggling. Which is what I said in my original reply to Merric.
Sorry to have given offense; hopefully that clears things up a bit!