True that the lower voltage heater draws more amps. But remember, you dont't buy power in amps, you buy power in watts (kilowatt-hrs really, which is just the watts x the amount of time you draw it).
Remember that WATTS = VOLTS x AMPS
So a 1500W, 100v heater (using 100 for simplicity) draws 15 amps.
But a 1500W, 200v heater draws 7.5 amps.
They still use 1500w to create the same amount of heat. The reason you'd want the 240V vs the 120V is because your electrical service can only handle so many amps, so you raise the volts of the heater and it draws fewer amps, thus saving more capacity for the rest of you shop/house.
A reason you might want the lower voltage heater could be for safety (110v is less dangerous than 220). But this becomes more important when talking about 600v industrial systems vs a 110v residential.