I think this is true with many amplifiers. The components need to warm up a bit to reach their designed operating temps. That's why a lot of uber-expensive amps have a "standby mode" that effectively keeps it powered up all the time so that it's ready for action on a moment's notice. The manual doesn't list the quiescent power draw. I suspect that draw is on the order of 100-200W, but perhaps someone from Outlaw can comment on the actual number.

Cheers,