We all know that logic and pokémon are like water and oil. In this series of threads, we will discuss the many unexplained mysteries of the pokémon world, by expanding it in our minds and imaginations to view ourselves in that world.
Mystery #4 - 6, only 6, no more than 6. Of course RPGs make a maximum number of characters in party since dragon quest, and pokémon is no diferent. But thinking outside the box, lets think of why could be the in-universe reason.
I go with Oak's explanation from Pokémon Special: Any trainer can carry more than six, but go over that number, and it becomes impossible to provide all of the care and attention for them.
Or it could just be a law to prevent people to walk around with more than 6 biological weapons in the belt.
http://en.wikipedia.org/wiki/Permaculture I also love jazz!