Let me put it this way:
In an ideal world where the rules are interpreted and enforced exactly as they could be by a very strict referee, on every single occasion, this would have been the result:
Studs up tackle - red (Pepe)
Intentional elbow - red (Messi)
Stomping a player on the ground - red (Marcelo)
Playacting - yellow (Pedro, Busquets, Di Maria, Dani Alves etc...)
Repeated playacting - red (Pedro, Busquets, Di Maria, Dani Alves etc...)
Players remaining on the pitch: 15
Out of all this above, only Pepe was punished. And now, I decided to not award yellow cards for complaining and shouting to the referee.
So why is this the case? Biased refs? Poor, but objective refs? The player's behaviour and/or reputation?