I have no doubt you've seen this.
When someone who isn't a real computer user sits down to use one, they stick out their chin.
You've seen this when your grandpa does it, or when some celebrity or politician does it at a photo op. Maybe you do it.
The Chin is a posture and an attitude.
In my experience, people with the Chin don't use a computer the way others do. They surf defensively. Not only does getting anything out of the computer take a little longer, but people with the Chin look for less and don't push as hard in their search for right answers or in their use of the tools available.
While there is a clearly a generational shift going on (watch out, here come a bunch of Chinless kids) it's also being driven by economics and social status and profession. Fortunately, it doesn't appear to be permanent.
[Update! I'm not referring to my esteemed readers with bifocals... the last three instances of the Chin that I witnessed were people who weren't even wearing glasses. All bifocal users are hereby excused.]