The reason they put the ten character limit is... Well, you're a good example yourself. You spam a lot, so we can already say that it has one good reason to be there (stop spam). Another reason would be that, frankly, this is a forum, not an IM client. You're NOT ACTUALLY SUPPOSED TO USE SO FEW CHARACTERS IN A POST. Rarely is an actual sentence composed of that few characters. That amounts to, what, one to three words?
The last time I checked, the messages you post with >10 characters actually constitute spam. See, Lowell goes a little overboard, but if you observe EVERYONE ELSE, you'd see that we aren't all spammers. True, we do spam, but when Andwhy says we're breaking rules, that's almost NEVER the rule he's talking about.