yeah... I really don't think Green Day sold out. When they started working on American Idiot, they really had no idea what direction it was gonna take them. It was something completely new for them (the rockopera thing and writing 9-minute songs) but to them it felt good and to them it felt like Green Day. If Green Day says their work felt like something Green Day, who are we to say it's not Green Day? So by the time they finished American Idiot, GD were totally excited about it coming out, but it was also terrifying for them in the way that they had no idea how people would take it, if they'd be slagged to death for it or not. Yet they still stuck to writing and finishing that record, thereby standing up for what they believed was the right thing to do at that time. The fact so many people appreciated that record and their believes, does not make Green Day sellouts. It just makes them succesfull artists who've managed to make a kickass record that shared thoughts and feelings with many people.
If they really were sellouts, they would have stuck to writing songs about masturbation and adolescence, because it's proven to be highly succesfull before.
And I also think that if Green Day's main goal was to make as much money as possible with their music, we would've had at least 2 new albums by now. :]