Yeah true that Google, Apple, FB have NY offices, but all of these companies are very HQ focused. Especially Apple and Alphabet, with most of Alphabet's based are based in SV (Calico, Verily, YouTube etc.). Apple is also notoriously Cupertino centric.
> The combined value of just Google, Apple, and Facebook is $1.3 trillion dollars.
Well, to the extent that those three companies have employees in other cities, I'd count their market caps proportionally towards those cities. I'm not sure offhand about Apple or FB but Google has a huge office in NYC. But that still leaves the vast majority in SV.
> Also, most successful hubs are often one industry towns. Think Detroit and Houston.
Ominous and timely comparisons. One-industry towns are also way more vulnerable in the long run. NYC is actually a counterexample -- it is the industry hub for at least three industries (finance, fashion, advertising) and leads or has a strong presence in many others, and it's been that way for a long time.
> But it is also a mistake to think SV is just a "tech" hub.
If being close to other members of the industry you are "disrupting" with tech is useful, then that is a huge advantage for a city like NYC with a wide variety of industry. But maybe that's not that necessary -- maybe Tesla would not get much advantage out of being in Detroit near other automakers. If that's the case then a city like NYC does not have any special advantage there.