well i was just at JFK this past week, not all flights show up on there every day, ex: I saw both Olympic and Austrian landing and didnt show up on flytecomm that day. Also, Royal Air Maroc doesnt show up on there at all. One day it showed Egypt Air landing at 3pm and it landed at 1pm.. so for some reason not always accurate, but still good enough for most things.
I don't live in NY so I really had to rely on flytecomm to know what was arriving, and I saw Austrian Airlines everyday I was there and one day it didnt show up, but it always lands around 2pm, olympic around 4pm.. Swiss and Austrian seemed to land on 31L when I was there, the rest of the european and other international traffic was landing on 31R. (if those 2 runways are in use) If you want to check out the departures go to www.flightarrivals.com