Perhaps other regions with a diversified economic base can never be as spectacularly wealthy, but they should be more insulated from industry collapse.
I think it's more that diversified, healthy economies take time to grow, and you'll never get the sort of fast growth rates that Detroit or San Jose have had in a diversified economy. Boston and NYC have both been around for close to 400 years; they've had industries rise and fall, which gives them a broad base to fall back upon when the latest industry du jour dies. Boston had a problem much like Detroit in the 1930s-50s when the textile & tanning industries moved south, but it also had grown strengths in education and finance (dating back to the 1600s) that served as the backbone for the tech & biotech revolutions of the 1970s an 1990s.
An interesting comparison might be with Salem, MA, which at the time of the revolution was the 6th largest city in America. Salem's growth was much more concentrated in shipping that neighboring Boston. So when technological development replaced sailing ships with steamships, which needed a deeper harbor than Salem could provide, the city declined until it was a mere suburb of Boston.
I think the strength of New York and Boston are due to a couple factors 1) crime never passed a certain tipping point at which most of the productive citizens left and 2) they both are traditional homes of industries that have done well the past thirty years ( finance and education). See my previous comment for the reasons why finance has outperformed manufacturing, - http://news.ycombinator.com/item?id=657765
Detroit is failing not just because its economy was driven by the automotive industry -- it was also dependent on a small number of employers (basically the Big Three automakers) who failed to compete with more agile, innovative foreign competitors.
There are certainly bigger players in the SV/Bay area whose disappearance would be felt painfully (Google, Apple, Oracle, etc.), but the business culture in the area also seems fairly able to turn collapses (SGI, AltaVista, Netscape, Sun) into opportunities, or at least mitigate the damage done.