Another reason the first album is normally the best is that the first album has years of touring, gradual improvement, self discovery and tour feedback going into it. A band can take as long as they like (funding permitting) to make their first album, and they can put that cool song on it that they wrote when they were sixteen - even if they don't release it till they're thirty. There is no such privelige with a second album, it has to be new to excite your fans.

On another note, selling out isn't always a bad thing. Sometimes a band can do more of the same for a big pile of cash or try and be inventive and new on their own again. I want this situation to change, but if I was given that choice I'd take the money and run.