Nassau County is suburban, Staten Island although being part of NYC has a very suburban feel to it.
Nassau County hit its peak population in 1970 (after doubling in the 50s) and has been declining since. Richmond County has about 50% more people than it did in 1970. People who were escaping New York have either moved to other states or further out on Long Island, while being replaced by people simply moving out from Queens or Brooklyn.
Staten Island is also more isolated, and residents may have a consciousness of being different than NYC residents. Nassau County was created from Queens County at the time Quuens County became part of NYC. IOW, it is just the other side of the settlement line around 1900.
Nassau's population did hit a peak in 1970 & dropped from 1970 to 1990, but has risen since then. The 2000 population was also higher than the 1980 population.
I think every downstate county grew from the 1990 to 2000 census. Upstate NY, on the other hand, lost 250,000. Places like the city limits of Syracuse and Buffalo have seen some serious decline.