The indie/folk/pop category seems a bit vague and better defined by what it's NOT than what it IS. It's also something that appears to refer, not simply to the music itself, but the artist(s) and history behind the music.
This song - The Longer I Run by Peter Bradley Adams seems a good example
Joshua Radin has a lot of great songs along similar lines. "Vegetable Car" may not be the best example, but I like it so hey, why not?
Is it possible for an artist to outgrow their "folk/indie/pop" roots? I assume so, and I don't claim to be an expert on the subject. In any case, Mike makes great music:
Anywhere by Passenger (A great performer and artist)
I know there are a TON of other artists that could be added to this. Feel free to mention some in the comments, if you'd like.