Its easy for the average good civilian whos never been in a dangerous situation to not understand such things so let me explain...

you see the BAD GUYS,.. are ALWAYS going to have the high capacity magazines..And when you get into a fire fight with them it quickly can turn into a game of whats called "Suppressive fire".. This is where the person with the most bullets keep shooting to keep the other person "suppressed", as they move forward and in an effort to get a good "angle" or "close in" enough to make their kill, you would be surprised how pinging rounds around a target will keep them confused and disoriented. HOWEVER, this can be countered by having an equal amount of bullets in order to suppress back and keep them from advancing, who ever runs out of bullets or gets the kill angle first...WINS...

In addition, getting shot at also makes you extremely LESS accurate, so a six shot revolver can miss everytime at the closest of distances.