If one of these were made for the US market it would obviously be configured to work at the US mains voltage and frequency. (Europe is 50hz, US is 60).
Your home's power input is also 240 volts in the US, regardless of being split into two 120 volt rails at the breaker box. It would be trivial to hook up a 240 volt system if you really wanted to, albeit not through one of your regular 5-15/5-20 outlets. You'd have to do it via a dryer outlet or something.
Watts are watts. If the unit is capable of feeding 800 watts into your home's electrical system, the voltage is irrelevant provided it can supply sufficient amps. A normal US household circuit is 15 amps, so a hypothetical US version of this thing would have to supply ~6-2/3 amps at 120v rather than ~3-1/3 amps at 240v. No big deal. It's not even close to maxing out a single residential circuit on either continent.