While I can see it from the bottom line on Activision's side, at the same time, they're at fault for these mid-tear games have little to no sales. They rush the work product to market, do little promotion of them once there, and then penalize developers on low sales.
I know EA has backed off from mid-tier titles, but at the same time they're open to a lot more risks, like Mirror's Edge and Dead Space (which has proven very successful).
It may simply be more that the "retail" market for these titles is waning - such mid-tier titles can't compete against CODs and Maddens and the like on the same shelf. But certainly plenty of room for titles when the publishing costs are kicked out.