I live in Seattle and have started 4 companies here. Prior to my first startup i was a VP for a large NY based software company, so while i have not lived in NY I understand the business 'culture'. The following are broad generalizations with plenty of exceptions, but in general:
1. shear mass (population): NY metro area is #1 (almost 6x the size of Seattle metro), Seattle metro #15.
2. risk averse: Seattleites just don't seem to have the same appetite for risk that New Yorkers have. Wall street is, after all, the legalized gambling capital of the world. while seattle may have the largest concentration of software developers and engineers (Microsoft, Amazon, Expedia, Boeing, Zillow, and a pretty strong biotech base, etc.) we don't have the financiers and investor mindset that NY has. the first generation of software millionaires came out of MS. Most MS millionaires were minted in the mid to late '90's. There were lots of tech startups started by and/or funded by new MS angels. Then the dot com implosion hit in early 2000 and these new angels and the few VCs pulled way back. MS stock bumped along pretty flat for the next 14 years. Those who had already cashed in their options were pretty gun shy about investing in startups. We lots of money here, just not in the hands of those with the appetite for startups. We still have a few VC firms, but they have not forgotten the startup dust bowl of the early 2000's. Compared to the bay area we are still toddlers.
3. "I want to give back to the startup community": Seattle tech millionaires don't seem to have the same connection to the startup community that you find in the bay area - I can't compare that to current NY. I'm not sure why that is. It could be that a lot of the local tech millionaires made their money from a relatively mature MS and Amazon and never really had an opportunity to experience 'startup' culture. MS felt quite entrepreneurial early on, but the 'adults' took over in the early 90's. Expedia is a great company, but it was never really a true 'startup' - it was an internal project at MS that got spun out on it's own. Rich Barton is a great guy and great investor, but it wasn't like he and bunch of cofounders had to live on ramen noodles for years. I'm hopeful that Zillow (also started by Barton) will eventually become a startup mothership. Given Jeff Bezos's entrepreneurial mindset I'm hopeful that Amazon will spit out more entrepreneurs and tech-investors.
4. NY wins hands down in the world of advertising, marketing and finance. Startups need 2 internal skill sets (minimum): product development and sales (or marketing if b2c). We have a pretty good supply of engineers here who want to start their own companies (still rather risk averse to joining others), but we don't have strong pools of experienced tech sales and marketing people here.
Again, these are pretty broad brush strokes, but that's what it feels like from the entrepreneurial trenches here in the silicon forest.