Show this to WotC Marketing...
I've been DMing for a few years, but have no particular love for any campaign setting. I don't care about their geographies, politics or histories if they don't mesh with the overall campaign we're going through. Which generally they don't because adventures rarely happen anywhere particularly important. Thus, things like the Players Guide to Faerun is lost on me -- it's just a hash of new races, prestige classes, and spells that I don't have time to absorb. I'm married, I'm employed, I'm a homeowner... and D&D is just a hobby.
But because I don't have time to absorb the plethora of new whatnot worth of overhead for said hobby, I prefer taking modules or campaign-sized pre-printed books with a mildly interesting plotline, using their maps (love Photoshop) and many of their encounters (love EL ratings) and twist the foundational event and style of that module into my campaign.
Now how are you going to sell me on an optional book that I otherwise don't want in my campaign? Demonstrate how dang cool it is in an adventure. Cross reference. Needing Monsters of Faerun for City of the Spider Queen is a good start. Magic of Faerun is likewise, but nothing from that book is especially highlighted for "really dang coolness". The hook to Song and Silence is kind of nifty, but isn't supported by the size of the adventure -- and S&S was underwhelming. But beyond all of that -- at least in the 3.0 release -- City of the Spider Queen absolutely demonstrated the niftiness of several FRCS prestige classes and, as such, effectively required that at least the DM have the ~$40 FRCS book (though sadly I didn't see a lot in the way of ties to the history/geography of the Realms which is the hardest part for me to homebrew on the fly...)
Compare that to Return to Elemental Evil which had only its own bonus material to work with. Return to Elemental Evil had no cross-merchandising for DMs to care about. Any bonus material players brought in was something that the NPCs didn't have available to them -- so it's easy for the DM to say "nope, doesn't fit in this story" and thus save a whole lot of money on splatbooks and geography books and the like.
I'm hoping that WotC is really making the hook-and-reference the case with the Eberron mods -- they can sell Eberron Campaign Setting books (dang expensive!) and maybe some Expanded Psionics Handbooks that lots of DMs would otherwise not use if it weren't canonized in the campaign setting. [Disclaimer: I don't play Eberron yet, but I think it's a pretty nifty goal to say "all of the rules are included in a sensible fashion", which is what I heard they were going for...] Eberron adventures need to highlight Eberron history, geography and culture. (So do Forgotten Realms adventures and the like, but I'm going off on Eberron at the moment...
)
Adventures are the gateway drug that introduces DMs to powerful NPC villians that use all of the optional rules, races, spells and feats and make their lairs in the secret houses of true power that only huge knowledge checks against a wide variety of campaign-setting historical and political figures can deduce. The most compelling and depth-intensive of adventures can have $0 margin and still make a killing for the publisher... but only if they're bait for the other products that the publisher has to offer.
::Kaze
I've been DMing for a few years, but have no particular love for any campaign setting. I don't care about their geographies, politics or histories if they don't mesh with the overall campaign we're going through. Which generally they don't because adventures rarely happen anywhere particularly important. Thus, things like the Players Guide to Faerun is lost on me -- it's just a hash of new races, prestige classes, and spells that I don't have time to absorb. I'm married, I'm employed, I'm a homeowner... and D&D is just a hobby.
But because I don't have time to absorb the plethora of new whatnot worth of overhead for said hobby, I prefer taking modules or campaign-sized pre-printed books with a mildly interesting plotline, using their maps (love Photoshop) and many of their encounters (love EL ratings) and twist the foundational event and style of that module into my campaign.
Now how are you going to sell me on an optional book that I otherwise don't want in my campaign? Demonstrate how dang cool it is in an adventure. Cross reference. Needing Monsters of Faerun for City of the Spider Queen is a good start. Magic of Faerun is likewise, but nothing from that book is especially highlighted for "really dang coolness". The hook to Song and Silence is kind of nifty, but isn't supported by the size of the adventure -- and S&S was underwhelming. But beyond all of that -- at least in the 3.0 release -- City of the Spider Queen absolutely demonstrated the niftiness of several FRCS prestige classes and, as such, effectively required that at least the DM have the ~$40 FRCS book (though sadly I didn't see a lot in the way of ties to the history/geography of the Realms which is the hardest part for me to homebrew on the fly...)
Compare that to Return to Elemental Evil which had only its own bonus material to work with. Return to Elemental Evil had no cross-merchandising for DMs to care about. Any bonus material players brought in was something that the NPCs didn't have available to them -- so it's easy for the DM to say "nope, doesn't fit in this story" and thus save a whole lot of money on splatbooks and geography books and the like.
I'm hoping that WotC is really making the hook-and-reference the case with the Eberron mods -- they can sell Eberron Campaign Setting books (dang expensive!) and maybe some Expanded Psionics Handbooks that lots of DMs would otherwise not use if it weren't canonized in the campaign setting. [Disclaimer: I don't play Eberron yet, but I think it's a pretty nifty goal to say "all of the rules are included in a sensible fashion", which is what I heard they were going for...] Eberron adventures need to highlight Eberron history, geography and culture. (So do Forgotten Realms adventures and the like, but I'm going off on Eberron at the moment...

Adventures are the gateway drug that introduces DMs to powerful NPC villians that use all of the optional rules, races, spells and feats and make their lairs in the secret houses of true power that only huge knowledge checks against a wide variety of campaign-setting historical and political figures can deduce. The most compelling and depth-intensive of adventures can have $0 margin and still make a killing for the publisher... but only if they're bait for the other products that the publisher has to offer.
::Kaze