There were different armor sets of each class in Diablo 3 revealed because these armor sets were found and pictured in the beta client of Diablo 3 itself.

These 23 armor sets aren't included in the beta but in the full game, while in the beta there are only one or two sets for each class. Blizzard wants to save up their content. If you wondered how your class will look like in the early or even in the late game, this is your chance to do so. My opinion is that the Barbarian looks best with his third set, and that's why I'm going to play a male Barbarian when Diablo 3 is released.