In either case, the end result is a world rich in flavor without a system to properly support it. Now we all know systems are important. Systems are the backbone of a game. They're put in place to help hold everything else up. The idea behind systems was to instill a reasonable degree of fair-play within a game.
Systems are fun to tweak and fiddle with, to bring out the most desired results.
Every gaming group I've run across uses 'house rules' with their games. In fact, most gamers design at least one in the course of their gaming life. Personally, I design game systems as a challenge to myself. To create a system that is easy to learn, playable, and yet fit into a game world is a challenge of math, creativity, and balance. Sure, I have dreams of actually getting a system published, I think most people who do design systems do.