On the Wikipedia page for the Boeing 757, it says this about the MTOW:

Maximum takeoff weight (MTOW): 255,000 lb (115,680 kg)

So my guess is that the normal procedures manual might be off. Especially when you consider that the aircraft.cfg has this:

[WEIGHT_AND_BALANCE]
max_gross_weight = 256000                      // (pounds)

Which is possibly the Maximum Taxi Weight, which, like it shows in the manual, is 1000 pounds more than the MTOW:

Weights	Pounds
Maximum Taxi Weight (MTW)	221,000
Maximum Take Off Weight (MTOW)	220,000