Yes, but that would only be drawn if you drove it at full level with a constant level signal - such as a sine wave. Music signals are just not like that, even with today's tendency to compress all the dynamic range out of the sound.
Whilst it is true that on loud peaks the system may indeed draw full load, it will only be for fractions of a second, and WRT rating of supply cables etc it is the average load that relates to heating effects in the cable and the thermal trip section of the MCB.
So in reality, the requirements of the mains supply are rather less than the rated output of the amp - even if they are quoting real watts. As BAS said, low end PA especially tend to overstate their output powers by a factor of 4 or more (they call it peak programme power or some such rubbish) because the people who buy them know no better and think that more watts=louder=better. Ask them about their speaker efficiency and they'd probably say "Duh!"
The way I see it, bands who want to play excessively loud do only to cover up their lack of talent and musical ability.
