I think he/she is saying labor rates are a supply/demand calculation, not a value one. The I-beam in your house might be the most valuable thing to the structural integrity, but it's probably not the most expensive thing in your home. Scarcity dictates that something else less valuable to your existence may cost more. You may not value that scarcity enough to pay that premium, but value alone does not set price. Air is the most valuable thing to my life, and I pay nothing for it.

So, a nurse or teacher provides a very valuable service, no doubt. Salaries won't naturally go up until availability goes down.