The 49ers don't need to blitz. They are getting enough pressure. They blitz just enough to keep the opposition on their toes. Remember, when you blitz you have 1 or two less men in coverage. They can be important in clogging the lanes and causing the QB to hold onto the ball and as you saw against Pittsburgh, there were several other times that we could have gotten at least two more interceptions if the defensive back was a little more alert. Take away that one or two for a blitz and you have less people flooding the field for those tip balls or if a defender or two misses a tackle. Which allows for the homerun.
Let's not get to excited, but Ben was hurt, he is normally when healthy hard to bring down and elusive for a big guy. Still when someone is a lame duck you have to take advantage and the niners did.