Barbarian is the most popular class. So, yes, the AH will be generally bought out by Barbarians.
However, in D3, all armor is usable by any class. Same goes for every weapon.
Though, there is some class specific gear, each class has 2-3 class only like barbarians use mighty weapons and mighty belts, wizards have orbs, monks have forehead jewel thingies, witch doctors have mojo, and demon hunters have cloacks and 1h bows.
Basically every enemy has a table of what they can drop (based on the area and level and difficulty).
The game basically does a series of checks when you kill something. First to find if it actually drops something or not.
If something will drop the game checks to see what will drop. Basically from the worthless trash to the rarest magical items that enemy can drop. The Magic Find ability basically helps push that table to the higher ends.
So having a 20% MF bonus doesn't mean that the enemy has a 20% increase to dropping an item, but rather if it does drop an item, when the game makes the check to see what drops the skill increases that "roll" by 20%.
So to make a very simplistic example, lets say 1-50% is regular white items, 51-70% is a basic magical item, 71-100% is a rare item.
If you have 20% MF, then if the game rolls a 10% when checking for what dropped, it counts as a 30%. You'd still get a trash item.
If the roll was a 47%, it gets pushed up to a 67%, which means you'd now get a basic magical item.
And so on.
Now the actual game calculations will work far more complex in reality, but that gives you a general idea.
Are today's games made for 1 armed, drunken kids with downs-syndrome? - krazy168 The politically correct term is "casual gamer" - wubikens