After some decidedly unscientific research I'd like to offer the following: Seattle pigeons are not as street-smart as New York City pigeons.
I come to this conclusion after passing by at least 3 road-kill pigeons in Capitol Hill in the last month. I don't remember ever seeing more than one or two smushed pigeon in the years I lived in New York.
This is one man's anecdotal evidence. But I'm sticking with it.