I believe the higher up the food chain slower the EP growth , this gives people down the road a chance to gain ground on the earlier starters in the game if this doesn't change it will be one of the major rasons for the games downfall.
The other reason is that it rewards people for farming kills and pushes some people out from completing quests. Why do a supply side production when I can farm off kills?  quests reward nice and getting something of a kill is allright , but should not promote farming kills in a production based game. Most items that are needed should be bought off they supply/production side of the game. Not off kills.