As far as i remember someone mentioned about some combination race class are irrational. Something about flying cow and DH.
Can you imagine big fat tauren or orc gently sneaking for prey? Elves are meybe a bit wrong example since we are learned by fantasy books that elves are stronger then human. But gnomes or goblins not. When you see in D3 barbarian's women you know she is able to lift heavy sword. It's many irrational changes in game made only for easier or better game experience. We don't need any big story behind.