I don't really put those two fumbles on Marshawn at all. The first one was just a perfect/perfectly flukey play by the defender, who got a perfect, blind shot that hit the ball just right. The second one was just hat-on-ball, something we see all the time from every back and something that's pretty hard to guard against.
I do think they should "conserve" him through the season, though, because his style is so punishing. He's a poor man's Earl Campbell.
Q: “What is your thing?”
A: “Lay back, kick back, mind my business, stay in my own lane.”