DLC is becoming quite a significant revenue stream for publishers. According to analysis conducted by Gamasutra staff writer Matt Matthews, Call of Duty: World at War map pack downloads have reached seven million. Back in August, Activision pegged sales at 6.5 million. With a two month gap, that estimation is rather conservative. And at ten a pop, that's a cool 70 million in revenue, barring licensing and distribution costs incurred on PSN on Xbox Live.
It's safe to say we'll be seeing multiple map packs for Modern Warfare 2.
Analysis: How Call Of Duty DLC Boosts Revenue, Publicity [Gamasutra]