I've lived in both NY and Silicon Valley. I think the best description of the difference in mentality is:
In NYC, if you can make a million dollars cool, but it's even better if you screw somebody out of a million at the same time. In Silicon Valley, if you make a million dollars cool, but it's even better if you help somebody else make a million at the same time.
look at all those happy/helpful people, ready to volunteer their time and emotional shares to help you get your project off the ground. (and this is only one great hacker spot in the city.)
in my experience (~10 years in manhattan+brooklyn)...these are the kinds of people/groups that are here...looking to build stuff and have fun.
...but, of course, in a place as large as this, you'll find all types. (as you do in the valley too, really.)
In NYC, if you can make a million dollars cool, but it's even better if you screw somebody out of a million at the same time. In Silicon Valley, if you make a million dollars cool, but it's even better if you help somebody else make a million at the same time.