While it's fair to say this is proverbially a quarterback's game, based on 3 out of the 4 wildcard games, it's also equally as fair to state that the importance of the running game (whether from the running backs or the quarterback) is just as paramount as the quarterback play as well.
Based on the games themselves, the winning teams' QB's didn't have much of any huge statistical impacts that many were expecting, especially in the case of upper-echelon QBs like Brees and Rivers.
Neither one of them had great games statistically by any stretch of the imagination (Brees was arguably bad), and yet their teams were able to come away victorious largely in part because of the play of their running games. The 49ers were really no different, but aided with big gains from their QB using his feet.
That's not to say that this isn't a QB's game as stated, but I think the playoffs are taking on a different animal altogether. Teams that are more than willing to go to the ground game even if their QB's numbers suffered because of it, even in defeat in the case of the Packers and Eagles, and have that balanced attack seemingly had greater levels of success than those that did not. Sans their injury situation, Kansas City not running the ball in the second half as much as they should have been was their downfall IMO
Ultimately, that is what it's all about in the playoffs in my opinion. Running the ball effectively and having your QB making timely throws when called upon and playing mistake free football. No game further exemplified that than the Chargers-Bengals one.
So, yeah, it's a quarterback's game, but the running game is just as important at this time of year too. Whether it stays that way remains to be seen going forward.