This notion has been around for thousands of years...

...Going back to ancient times, it used to be the landed/noble classes that looked down on the jolly numbers; now a lot of the divide seems to be about whether one makes a living using muscles above or below the neckline.

I agree with those who note below that you can make a darned good living in a blue-collar job. My only caveat is that I know a lot of people (myself included) who moved to using the muscle between the ears a long time ago, and if the mind and body hold up, could continue to work full or part time making a good $ until age 70, 75, even 80, if one chose to.

You don't see many 70 or 80 year olds swinging a hammer, doing plumbing, or cutting sheet metal ductwork. So part of the elitism might be that those of us who do mental labor will consciously or subconsciously pat ourselves on the back (or however you'd put it) for not having to subject our bodies to the kind of physical stress that factory workers, carpenters, plumbers, et al. go through every day.