I find it unfortunate that d20 publishers do not create more adventures, for purely selfish reasons - as a DM, I run a lot of published adventures (about 1/2 my adventures), mainly because I don't have the time to make the stuff up like I used to.
BTW, I prefer pdf for adventures, so there may be some point to pdfs cutting into sales (I purchase those I play, but I have no idea how many do). So do all the past adventures, which are still available and cheap (like the AD&D ones).
That said, when looking at the products that sell I see some leading companies producing adventure/settings combos. Malhavoc Press, Necormancer Games, and others all seem to make many adventures or adventuer-containing products, and (to an outsider) seem to be doing fine. I can only hope that will encourage future publishers to produce more adventures, though I think those will be in the more sizable sourcebook-adventure model.
I actually prefer the short-adventure model; less of a hussle putting it to use, is over quicker, and I need to read less (did I mention I am pressed for time?). But from what the publishers here told us, this is not selling well.
Another encouraging trend I see is the publishing of very small pdfs, containing just a few pages, for very cheap. So far these have focused on "a dozen new Xs", or "palaidns and clerics in 20 modern", or similar gaming tidbits but IIRC several companies are starting down that road. I can only hope this extends to small-encounters, locations, and plots - small adventures, that can provide the core of the adventure while I fill in the blanks. Frankly, that kind of product would be ideal for me.
It is ironic that the trend in published books seem to aim to larger and larger pieces, while in pdfs there is a trend for lighter one. Or perhaps I am just seeing things that aren't there.
I would like to thank the publishers for being frank. So thanks.
In hopes of greater, better, adventures,
Yair