Direct2Drive has word they will not carry
Call of Duty: Modern Warfare 2 due to its use of the competing
Steam service. There's a statement about this on
Gamasutra where Direct2Drive says: "We don’t believe games should force the user to install a Trojan Horse," referring to Steam.
Voodoo Extreme also notes that online retailers GamersGate and Impulse are following suit, with Impulse saying: "The most obvious issue is the forced inclusion of a competitor's store that blocks us from carrying the game."