Rovio's Angry Birds is free on the Android Market, though it costs $0.99 in the App Store. When asked why it is free on Android, Rovio Tweeted, "because that is the google way;-)." By that, Rovio meant that the majority of apps on Android are free and ad-supported.
Meanwhile, the company also Tweeted the news about the milestone: "We just hit 7M downloads on Android."
At the same time, despite the fact you know that Microsoft would love to see Angry Birds on Windows Phone, it's not going to happen in 2010 (or at least, is highly unlikely). Also Tweeting a response, Rovio said: "never say never, but it's highly unlikely."