[KaVir]

It's to encourage people to move on to new challenges. If players had no incentive to leave Newbieville, they'd just stay there, killing the same old rats and worms, over and over - and that's when it starts feeling like a grind.

Yeah I agree it's silly to die to a rat, but that's really a cosmetic issue. You could rename the rats "bandits" without changing the underlying system - kill X, get stronger, move on to Y, get stronger, move on to Z. This is a tried-and-true way of getting players to gradually advance through all the content, one step at a time, so they feel as if they're making progress without being overwhelmed with too much at once. Most tabletop roleplaying games work this way as well - even in the World of Darkness games you mentioned, players typically face stronger challenges as they progress in order to give them a sense of achievement.