It would be easier to name bands who HAVEN'T lost their creative edge. I think it's the natural way that it works - you start off with great stuff and then over time you start to suck. The longer you continue to put out records the more mediocre they become. I don't think it can be avoided. Every band manages to start making boring records and the original fans start giving up on them. It would seem to make more sense to quit when you're ahead, but it doesn't usually work that way. Perhaps it is impossible to be aware of one's own suckiness.