OverRun has summed it up quite nicely, each airport is specifically assessed, we dont have any fixed rule stating that we will not operate the B747-200 into runways less than 2100m.
In fact we operate into Rome and Paris where the runways are close to 2100m without any complaints. The runway which causes the most complaints is 3100m without any obstacles, the takeoff weight is limited by the accelerate stop, we operate 10 hour sectors from there at the maximum weight. The runway end and those red lights appear quite close as you run out of tarmac.
Mutt.