W the derived SI unit of power, equal to 1 joule per second; the power dissipated by a current of 1 ampere flowing across a potential difference of 1 volt. 1 watt is equivalent to 1.341 × 10 --3 horsepower
Watt | Define Watt at Dictionary.com

The way I read that...in our audio applications we're talking about heat dissipation as the primary concern.