That's true, but sort of misses the point. Most regions have a dominant industry, and these industries change over time. Silicon Valley, to take your example, used to produce actual silicon devices. Los Angeles used to be a major petroleum exporter. Those jobs left, but no one cared.

People argue over "appalachia" and make false promises about coal (coal is dying whether anyone wants it or not -- other sources are simply cheaper now) because it workers a swing demographic in presidential elections.