If you think that PFT is the core reason for the devaluation of the industry you are dead wrong. If there was a pie chart to show its effect I would be surprised if it was anything greater then 1%. To name a few for declining wages let start with the following.
Bankruptcies
Oil's unexpected rise
911
Deregulation
Outsourcing
stagnate or negative GDP
LCC's
regulations
I can see Richard Anderson in a board meeting telling the union that they aren't going to pay out because people are willing to buy there job. There isn't any industry right now that isn't trying to devalue the American worker.