I think you've misunderstood Gaston, He's asking why you need to drop the voltage as you normally do in an amp circuit, Then send it out to your speakers giving you less 'power' when you could theoretically just send your Mains 120Volts to the speakers giving you a 'Mega silly ammount of watts'. His 1800 figure is the figure he's worked out in Watts which would be delivered to the 8 Ohm speaker from a 120V supply.
He hasn't mentioned stepping up the supply voltage to 1800 Volts. I get where he's coming from, but totally agree that it would be just as silly as the 'Mega silly ammount of watts' to even contemplate driving a speaker directly from a mains supply without isolation, Otherwise you have a speaker which is sitting at mains potential! As already stated by Audioguru.
My 2p worth anyway!