Ed,
What makes you think the Wattage remains the same if you increase voltage? That would depend on the appliance design wouldn't it?
ORIGINAL: NM2K
Many folks sort of know that for a given wattage, higher voltage means lower current. Additionally, lots of folks who are not electrical professionals have also heard about I square R losses and realize that running a higher voltage for a given wattage, with its reduced current, is more efficient than obtaining the same wattage with lower voltage and higher current.
Ed Cregger