I'm not sure whether innovation and growth is the key to success in this field. Looking at the trends it seems like there's a natural saturation point where you reach max penetration, followed by an exodus. I really doubt it's possible to keep the ceiling going.
I don't think you can compare MySpace and Facebook. MySpace never really innovated. They never had a platform or began to do what Facebook did. They got bought out and lobotomized.
You're right. I posted it because the Myspace<->FB comparison is often used and I wanted to illustrate the trends for something that grows/saturates/declines.
Facebook started sprinting and never stopped.