I don't think people don't act, dont get me wrong, especially in LARP. I just deny the notion that acting for a character happens on the same level as talking in "real life" when you are just yourself. There is always a margin of creative thinking involved - unless you did years of hard theatre training or are a rare super-talented actor, but I think its fair to assume that this is not true for most RPlers. Or you do actually talk as in real life, meaning you are not actually acting at all, just adding a slight "Aragorn" flair to your own.
Also RPGs are improvisational which is even harder to act. Theatre and movie actors do extensive scene and character studies, improvisational actors don't have that luxury. This makes it even more clear to me that the average Joe RPGler don't think and speak on the same natural level as when being out of character - if they actually try to act and roleplay and not just be themselves.