Probably a calculation/editorial error. I just found an error in the cauchemar nightmare's carrying capacity--the MM editors failed to factor in its bonuses for size and being a quadruped.
I think the only reason weights are given for creatures at all is for the telekinisis spell. I don't see any other reason for the obviously arbitrary weight rating Wizards tried to apply to all creatures.
Well, if you assume the flesh of demons and devils to be as dense as human flesh, both are way off.
A 6ft human may have 200 pounds.
A 12ft tall being would be twice as tall, twice as wide and twice as "deep" as a 6ft being, so it should be eight times the weight. So your average 12ft demon or devil should be at least 1600 pounds, perhaps closer to 2000, as they both are depicted as being very muscular.
Have a look at giants: Stone Giants are 12 ft. tall and average 1500 pounds, fire giants are 12 ft. tall and average 7000 pounds! The stone giant is ok, as they are described as gaunt, but even the barrel-chest of fire giants don´t give them four and a half time that weight. The values seem to be amiss here.
(As a note, most devils seem to be relatively lightweight).
Stefan
Baatezu: Empty Souls, Empty Calories...
And that is what accountancy does to you.
...and the obligitory...
Tastes like chicken.
EEEEEEEEEEEEvil chicken