I think those who find it an astonishing revalation that WotC benefits from 3rd party publishers ought to step back and learn a little economics and history associated with the situation.
In short, the game benefits from support as a whole. But small print run items are not profitable for a large company like WotC. They have salaried employees and other fixed cost items, has an upper management that is not risk-tolerant (anyone remember the forgotten rums stories), and has certain expectations of profit margins. In short, WotC could not afford to support the variety of lines that late TSR did. Note that WotC has cut back to two supported setting lines for D&D, compared to all the ones TSR had. Word had it that the cut off number in late TSR was 5000 copies minimum to even think about printing it. I suspect that WotC's standards are higher than that.
So, in essence, what is WotC to do? Third party publishers are a form of outsourcing. Most third party publishers don't report to corporate bureacracies. Many third party designers don't do this as their day job. They can "afford" (yeah, I know, some can't) to put out smaller print run items and give the customers support that WotC could not afford to provide. Further, if the skaff effect is to be beleived, the variety offered by third party products helps keep players in the network and reduces the inefficiencies of players returning from other systems. And networks are vital to WotC's strategy.
So if you see the situation as "every penny that a third party publisher got could have been a penny WotC got", you are preceding from a faulty assumption from the outset.