From wikipedia: 'Some combat sports (such as boxing, judo, taekwondo and wrestling) award two bronze medals per competition, resulting in, overall, more bronze medals being awarded than the other colours."
The occasional tie could also push it the other way— an additional gold at the expense of a silver or likewise with two silvers instead of a silver + bronze.
From wikipedia: 'Some combat sports (such as boxing, judo, taekwondo and wrestling) award two bronze medals per competition, resulting in, overall, more bronze medals being awarded than the other colours."