Originally Posted by
Kisho
Because flavour, uniqueness among classes, and who cares when you're less than 90 anyway.
The first two are important because people like to feel special and different. Have you seen how much people cried over 'class homogenization'? Anytime we take a step towards making classes more similar, we risk invoking that whine again. And to be fair, it is somewhat valid. We don't want classes to be all the same, and they're not. But you have to be careful with anything that makes it seem as though we're going in that direction.
The last one means buff inconsistencies aren't important. Prior to level 90, class balance just doesn't exist. It's irrelevant, meaningless; the only time you really need to worry about buffs is in high end PvP and raiding. As such, to appease those who care about feeling like a special snowflake, Blizzard gives us a difference in classes whilst levelling. A small difference, but a difference nonetheless.