A Watt is a watt is a watt, whether you get it from 110 volts, 150 volts, 120 volts, whatever you call it in your area, or 220 volts.
hell if voltage is the key, using that logic why don't you just forego the stepdown transformer and get a cooker that will roast beans at 4160, or perhaps skip another transformer and do a 33.6K cooker? Aww hell, why not just take it right off the tap and go with a 220KV cooker, don't stand closer than 5 feet though or you might become involved in the cooking process.
The only REAL reason folks use 220 is because of the power needed, not because it's better or cleaner power, it all comes from the same transformer, from the same fusebox in your house. Household wires for 115, are limited to carrying about 15 amps, sure you can get a 115 volt 30 amp circuit put in, but you will pay for that extra copper. It will be stable as hell too.
Generally things at about 1800 - 2000 watts swap over to 220 so there is less current draw through the lines, it's the amps that cause the unwanted heat. Higher voltage = less amps for the watt hence less heat loss... all other things being equal.
why does the usa use 115. Umm good question, it is safer than 220 really... yes it does kill a lot of folks but if you get hit by it by mistake, your chances of getting back up, possibly cursing and walking away are a lot greater than getting swatted by 220, 277 or the likes.. Higher voltage pushes the amps, and the amps are what kills.
For home roasters, your residential 110 volts will work fine with a 110 volt coffee roaster if all else is good. If you get a voltage drop on the 115 you are going to get a bit of a drop on the 220 as well... if the drop is caused by insufficient wire load handling ability then that is a fault with the wiring, NOT with the electricity being supplied. BIG difference there.
Before we go running out to put in brand new dedicated circuits, spend hundreds extra on 240 volt stuff, etc... check that the existing wiring is not the fault. If you live in a 50 year old house with 50 year old wiring, umm guess what... the electrician who puts the 'new' stuff in is probably going to tell you the entire house needs rewiring to conform to code if you want the job done correctly, and might even refuse it....
Instead of 16 ounces of beans, try 14 or 13 ounces, ... sometimes little things are a lot easier and a lot less expensive of a fix.
aaron