Yeah exactly, I mean how would you feel if you found out you got down voted on an answer you wrote ages ago, that was correct at the time but since Game Freak changed the game mechanics it's incorrect in the current Generation? Not very happy I imagine? If an answer's outdated it's better to leave a comment telling them it's outdated than down vote them, as it's just being a bit more considerate towards people's answers.
But yeah you can up vote and down vote whatever you want, just obviously try not to spam up vote/down vote.