Jim Harbaugh has changed the culture of the current San Francisco 49ers team, which leads to the one, core thing about this team that is different to last year's.
He has them playing loose.
While Mike Singletary ruled over the team with dictatorial fear, it became clear that his coaching style didn't work with the psychology of this team.
Not only did many players and even a GM jump ship, but the team played so tight that it couldn't help making mistake after mistake after mistake—especially when the game was on the line.
Singletary was the great player who couldn't understand why all of his players couldn't play perfectly when perfection was demanded.
Jim Harbaugh was less of a player and understands how to foster a nurturing atmosphere.
Harbaugh's respect for his players on and off the field has put the 49ers at ease. This ease is allowing the team to perform and, more importantly, execute at a higher level.
This doesn't mean Harbaugh has any less expectations than Singletary did. Rather, it's that his way of going about it is already proving more effective.