More controversy is brewing surrounding the release of Modern Warfare 2. Apparently the game forces you to install Valve's Steamworks with the game itself. That's gotten Direct2Drive a little upset.
Direct2Drive directly competes with Valve for the digital sale of games hence the problem. D2D told Kotaku that, "We don't believe games should force the user to install a Trojan Horse."
Before you freak out and say that D2D just called Steam a Trojan virus, keep in mind there's a greater literary reference behind that. I'd guess he just means you're getting something hidden inside the game.
Other digital distribution retailers aren't selling the game either. Impulse and Gamersgate confirmed to Kotaku that they won't be carrying Modern Warfare 2 either.