There has been recent speculation on a blog post (http://blog.seattlepi.nwsource.com/digitaljoystick/archives/122799.asp) stating that Bungie was to leave Microsoft. Then a while later after many people ignored it as nothing more than a hoax, the unthinkable happened and Bungie and Microsoft put out an official press release (http://www.bungie.net/news/content.aspx?type=news&cid=12835). Bungie have said that Halo 3 was to be their last title in the series, and are now already working on their next game. However, Microsoft still has plans to milk the franchise with the RTS game ‘Halo Wars’ created by Ensemble Studios, and a hushed series of games from newly created studio, Wingnut Interactive in New Zealand, led by Lord of the Rings director (and Halo film producer) Peter Jackson.
Personally I think it’s great that Bungie have gone independent. Just look at companies like Insomniac Games, they still make games for their respective console, but they are given more rights, and creative freedom to shape their games how they want them to be, without being pressured by companies like Microsoft, Sony or Nintendo. I bet Bungie were just getting a little tired of Microsoft pushing Halo down everybody’s throats.