So...do they use their own Pokemon game? Also...World Championships? Really?
You would not believe some of the insane math that goes into proper training.
See, Pokémon have genetic values, which they inherit from their parents, up to a value of 31. That means they have 31 points more in a stat when at lvl 100. Considering stats go up to 300 or so, that's a lot.
Then there are also Effort Values, which further raise your stats depending on which Pokémon you beat (e.g. if you keep beating Chanseys, it raises your HP, I think.)
And of course the different items the Pokémon can carry, which influence their stats, moveset, or do something else entirely like hurt the enemy on a physical attack.
Then double fights add a whole new level of complexity. For example, you can have very strong attacks like Earthquake which hurt all Pokémon except those who have Flying type - because they are, duh, flying. So what you do is send out your Ground Pokémon and a Flying Pokémon and let them rock the enemy to pieces.
...excuse me, I only have a vague memory of the last five minutes. I geeked out again, haven't I?