Perhaps they needed help with promotion? Anyway according to Rovio's press contact Ville Heijari, they used Chillingo to reach the US market. Rovio and Chillin

Perhaps they needed help with promotion? Anyway according to Rovio's press contact Ville Heijari, they used Chillingo to reach the US market. Rovio and Chillingo had a deal for two versions of Angry Birds for iOS. Angry Birds for Android and upcoming Angry Birds Halloween (for iOS) are published by Rovio. They own the brand and develop for other platforms by themselves. Also in case you haven't heard, the Angry Birds brand is expanding quickly. Soft toys, movie etc. All of these require contacts and expertise, which Rovio did not possess at the beginning of the journey. The game itself wasn't as cheap as you might think. I've heard that they poured a few hundred thou into developing it.