Then to be fair, I'll use the heatsink-cooled, class AB, Behringer A500 as an example. 18lbs and it outputs 220 watts x 2(440 Watts), measured, without clipping, into a 4 ohm load. Two of them is only 36lbs.
It should not be difficult to get a true 100 x 5 watts, for well below 50 lbs.
-Chris