More of a trivia question. I'm an EE, so I think I know the answer. Nevertheless, I'm surprised that the 24 V flavor of the Multiplus doesn't put out more power - or doesn't hold up better at high temperature - as its 12 V brother.
I was expecting, given half the current input for the same power out (and so less I^2*R loss), that the 24 V unit would be rated higher.
I presume that the bottleneck in output power is not the input side of the transformer, but rather the output side? (Since 3000 W at 120 VAC pushes the same amount of current through the transformer in both versions.)
Still, there shouldn't be as much heating of the transformer core proper, since the heat generated at load on the input side of a 24 V unit is less than the heat generated in a 12 V unit.