I routinely see help wanted ads for skilled machinists in this area, and the advertised starting rate is anywhere from $12-20 per hour, DOE.

Now, you're a new machinist, and you walk into a machine shop getting paid $12/hr.

Someone gets Wal-mart to go with the mythical $15/hr wage. Is the machine shop owner going to give his employees more money to beat the retail starting wage? To do so he would have to raise prices to his customers, and the snowball effect begins, with inflation eventually negating the value of $15/hr.

You can't artificially inflate the value of unskilled labor without waterfall effects throughout the economy (AKA inflation) If you want to earn more, get a skill, learn a trade. There are apprenticeship programs available with want ads for apprentices. No, an apprentice tradesman doesn't make much over minimum. A Journeyman, however, earns much more than that. Why? He/she has acquired a skill with value in the marketplace.