Cedric: I actually have a character whose stat run like this: 18 17 17 16 16 16. Of course, he's what I call my "Oh $h!+!" character, because he oftent does things that basically make his opponents say (and do) just that. Example, very first encounter he had in the campaign, he was skewered through the armpit by a big harpoon. Instead of laying against it or falling unconsious (as a normal, mortal character would), he litterally walked along it until he was free, then decapitated the thing that had skewered him.
Now, back to on topic, you may or may not want to balance the party. If you're group's any good, everyone involved that anything that happens in game is in game only. If they don't feel this way, make them sign a contract saying just that, that in game issues stay in game, and RL issues stay in RL.
And another idea: the Stat Pool system. You need to determine how many people are going to show up, then roll up enough stats for everyone, using whatever method you want. Present the group with the numbers, and have them work together to build a party based on those stats. It should make a noncohesive group work together a lot better.