Everything else being equal (and in reality it never is) the reason that large amps are very heavy is they have very heavy transformers which you really need to get high quality power and things like subterranian bass.
Unless of course your amps have superb, richly toned and articulated bass, reveal hand built quality, output 135 watts into 4 ohms, have *no* transformer, and weigh in at a paltry 35 pounds each. I suppose this is the vanishing equality part of reality you were getting at. :-)
Cheers,
Tim