G'Day Ba's; Someone knows why some beer competitions like AIBA give multiple silver and bronze medals in each category??
Because the medals aren`t necessarily awarded to the first, second, and third place entrants. There are certain stylistic criteria set out for the different categories by which the entrants are measured, and beers that achieve a certain level of excellence when measured against these criteria are awarded medals based on how well they measure up.
At competitions like this you find multiple metal winners for the same class, but it is the "Best of Class" and "Best of Show" awards that you should look out for. Or in the case of the CA state fair that hands medals out like candy, but it is the 1st, 2nd, and 3rd ribbons that really count... Just another way to help people sell beer my good man. "I won 11 gold medals! And so did everyone else entering... but don't worry about that..."
Different judged events use different award formats. Non-beer related, but at the wine judging Monde Selection in France, the biggest award is a Grand Gold - unlike an ordinary Gold award, for a Grand Gold all judges on the tasting panel assessing the given wine have to unanimously agree the wine is a faultless expression of its given style/varietal/appelation. Given the subjectivity of taste, I think that's a pretty neat standard. Do any of the major beer awards do something like that?