Got those mixed up Jona. The aircraft needs more runway for the T/O because IT IS fully loaded. It hasn't burnt any fuel yet due to not flying yet... The problem in this situation is the lack of runway TODA (Take off distance available).
DC-8/707 are a bit different then modern jets, Jordan
at least the DC-8-10/20 and the 707-120/220 needed nearly the same distance to land as they needed for T/O at MTOW, while nowadays most jets need less than 50% of T/O rwy to land...
You are right that IRL the 707's and DC-8's needed a lot of real estate to land for the reasons you mentioned, but in this AWS case the flight is able to operate fully loaded from OAK-LGA but is limited to 7 passengers from LGA-OAK, so the short 7,000 foot runway is limiting the MTOW and therefore the useful payload on departure.
Damn, just saw I switched the routes, thought the OAK-LGA was limited...
Anyways, LGA is not useful for any long routes, due to its runway.
In reality KLGA is limited to max. 1500NM routes due to legal requirements.