Greg, I'll second Les on this, mostly. In terms of vacuums (universal motors) there is not an appreciable difference. You could take a UK or EU vacuum and run it fine on a North American 240v supply.
Let me break it all down. The UK uses 240v at 50Hz. Most of the rest of Europe use 220v at 50Hz. Because of the EU, there is a slow movement to meet in the middle at 230v. The UK agreed to this, and they are 'working' on it. However, they've written legislation that allows them a 10% margin of error, so they can just leave their voltage at 240v, but say they're at 230v lol. North America uses 240v at 60Hz.
For a vacuum cleaner motor, the difference would not be noticeable between 220 to 240v, nor from 50 to 60Hz. Even if it had electronics on board, they're largely designed with a 200-250v tolerance to cover all of Europe. That's not even mentioning local voltage variations. In America, all appliances are designed to work from 110-120v, just for line variations. European appliances will of course also have a tolerance.
As for line frequency, it would affect an induction motor, as they need to be designed specifically for a particular line frequency. But vacuums (outside of central units) do not use induction motors, they use universal motors. 'Universal' here meaning DC or AC at pretty much any frequency. There is an upper limit to frequency, but we're only talking a 10Hz difference. Look at an old vacuum that says something like '0-60Hz.' If a machine has electronics on board, they run on low voltage, which is made by rectifying line voltage to DC, so the frequency is removed entirely. The same would go for a BLDC motor's controller.
Les - you CAN actually double up two 120v lines that are out of phase with each other. They HAVE to be out of phase with each other, it simply won't work if they're not. That's exactly how your stove or dryer outlet is wired. That's exactly how that $220 'voltage converter' works. It's literally just two extension cords wired to a box that takes only the line wire from each and connects to a 240v outlet, and thus safer.
Also, the higher the voltage, the smaller wire is needed to carry the same wattage. So imagine in Europe, their wires are half the size of ours, for the same duty. So actually, with the higher voltage, the same wires meant to carry a given wattage on 120v, would be twice the size needed to carry that wattage on 240v.