One Twitter or Facebook can hire as many engineers as 1/2 that list. To say nothing of other interesting, top-tier tech companies from which there's nearly a limitless need for more engineers.
I have good friends who are good engineers in NYC, and I live here in SF. They had a ton of choices from digital agencies, finance companies, and myriad other places building line-of-business software. Here? Every experienced engineer I know with a LinkedIn gets several cold-inmails a month for startup & tech company opportunities.
It's about density. The financial district in San Francisco can fit in about 1 block of lower Manhattan. And the startup community in NYC compares similarly to the startup community here -- which stretches 50 miles from San Jose to San Francisco and beyond.
I know this is a silly argument, but unless you have some evidence, I would advise you to take that back. http://nytm.org/made-in-nyc/