I'm going to guess that ATC have a/c at those altitudes purely out of necessity. That whole area is a hornet's nest and they need any and all airspace. If an aircraft is there, it's probably because there is another aircraft at the more-desirable altitudes. As you probably know, it's not just the "big 3" in that area. There's TEB, ISP, Stewart, and all the other smaller airports so there are a/c everywhere. I don't have a lot of experience to LGA or JFK but tons is EWR and SBJ is only used as a departure fix out of EWR.
As for speeds, 250 is the norm on the departures and anything from 180-250 on the arrivals. Usually, the departures are 250 because ATC wants you out of their hair. Sometimes it's a little slower but that based on the a/c in front and required spacing. The arrival speeds is dictated by volume and required spacing.
Last edited by Bloodhound; 09-16-2007 at 08:23 PM.