Returning punts and returning kicks are two completely different responsibilities. Kick offs are normall drama free. You don't have to make a catch in high traffic. This is perfect for a true freshman to get in the game and try to make a big play (ie Dontre last year). Punts on the other hand, more times than not, are having to be caught with guys flying at or around you. Much more decision making must take place. It is normally best to have someone with experience, even if they aren't as dynamic of a play maker (ie Philly last year).
With that being said, I can certianly see Samuel or Johnnie Dixon returning kickoffs this year. Punts is still up in the air in my opinion. Maybe Dontre. Maybe James Clark. They have both been here a year. Maybe the trust a guy like Marhsall's decision making enough to put him back there.