Over the past couple of years, a lot of publishers were persuaded by an argument like this: "Why not use DTRPG as well as RPGNow? Sure, we get less money from each sale," they said, "but it's extra money for no extra effort!"
The answer to "why not" is the same answer you get when you ask "Why shouldn't I discount to some customers? I'll get extra sales today, and I've already broken even on the ones I sold at full price."
The answer is that the people paying full price say next time, hey, we want that deal too! Or, because as middlemen the "full price" folks are at a competitive disadvantage (either because they have to charge more than the people you give the deal to -- like Walmart vs. local shops -- or because they don't have as big of profit margins to reinvest in their business), they suffer business declines and can afford to buy less from you at full price anyhow.
It hurts to have to pay more now to both, but the publishers had to see it coming. Signing on with DTRPG was telling the other PDF distributors "you can charge us more". You can be sure that OBS will be able to charge yet more in the future -- after all, the extra margin will allow them to grow the business, which will justify an even bigger margin. (Would you rather get 50% of 200 sales or 65% of 100 sales? Besides, you can still sell it on your own website, so those extra sales are just free money, sales you could never make yourself without the big site's reach.)
DTRPG has played this very well -- first attracting some big publishers with the soothing assurances of DRM, to get their toes in the PDF pool (and holding on to them with exclusive contracts at the start); then attracting the independent PDF players with the promise of incremental revenue, per the argument above; and now merging with their biggest competitor. Just like when eBay hikes its fees, there will be grumbling, but almost all of the frogs will stay in the pot, as it were, because it still looks better than the immediate alternative.
The cherry on top of it all is that OBS is turning publishers' reasonable fears of future commission increases into another benefit for themselves, by offering publishers the chance to lock down today's rate for a term of their own choosing with an exclusive contract. The more publishers who hedge against future rate changes by writing long durations, the harder it will be for any serious competition in the market to take hold and forestall those increases or reverse the trend. (They make it easy to sign the exclusive by letting you sell on your own site -- because those sales won't be a threat to them like a rival aggregate site offering dozens or hundreds of publishers could be -- the kind of threat that DTRPG and RPGNow offered each other as rivals.)
But if you're a publisher, what can you do, given how much of the market these two sites represent today? Even if you weren't lured in by the siren call of incremental sales, your fate was decided by those who were. Most of your sales probably come from one or both of these sites. The rational thing to do is to submit to the changes, and hope that the promise of bigger total revenues in the end is delivered. In order to resist the changes there would have to be a massive rejection of the merger by many publishers, changing the numbers for OBS to the point where they would calculate that they would make more revenue in the end by retaining all the publishers, even while taking a smaller cut from each (after all, the added cost of having those extra items in their catalog is trivial, so if you can have them in the OBS catalog it's like extra money for no extra effort). Given the number and size of publishers necessary to change that equation, is highly improbable that such a thing will happen.
-John Nephew
President, Atlas Games