I guess depending on how broad your definition is, then it my scenario supports your assertion. All vocational people have a training period (modern version of an apprenticeship).
I'm not sure a lot of IT is actually that safe. Companies have a lot easier time outsourcing IT to another country then welders. Silicon Valley has inertia and good laws to foster innovation and startups, but others can change their laws and unfunded liabilities of the state government might not allow for stable conditions long term. SF's attempt at taxing might not be an anomaly but a trend.