Great Article by Glenn Dickey. Basically, he says that there are two types of successful coaches: Those that come in with a philosophy and get the players to run that system. And there are coaches who adapt to their team.
According to Dickey, it looks like Sing falls into the second camp. He then goes on to lay out all the reason the spread is perfect for the 49ers:
1. QB w/ a history in the Spread
2. Poor pass protection. Easier to make quick reads out of the spread.
3. Poor run blocking. RBs have more room when running out of the spread -- Gore had a great game (5.5yds/carry)
4. Emergence of Crabtree and Hill to compliment Davis
5. What've you go to lose??? You're 3-5. Better find a way to win....fast.
Lynch says the same thing: