Other locales have spokespeople who talk about how they are desperate for programmers and how great it would be to work there. Then you find out the reality and it's 50k top salary programming tps reports in an office park in the suburbs.
(B) Many more creative types than just developers are attracted to NYC such as fashion, tv, finance (if you don't think CDOs are creative then look closer).
(C) Because of the diversity of people you get really interesting experiences and ideas you couldn't get anywhere else. The Bay Area's idea of diversity is hackers that like to wear black t-shirts vs VCs that like to wear Polos.
(D) For being a much bigger city, New York is much more compact time-wise because you don't have to drive everywhere, which makes it fundamentally more liveable.
And (E) as for Boston, as an MIT alum currently still in the Boston area, I can tell you that nobody wants to stay here after graduation....the city is tiny and the bars close at 1 AND it's freezing 8 months out of the year.
Another amazing thing about those jobs is that they want you to sell your house, probably at a loss, and move to their obscure location, but they don't want to pay any relocation expenses.