Well, I dunno, do I? Hey Mr. Britain, I've not got your counts for sure. Nowhere above did I state what I paid for a fine SE-A70, only what they go for. I bought mine from a military USN from Japan that bought it in the later '80s. Gold fetched a lot less in the '70s too (SE-9600), which time I lived in Cheltenham, Bucks, and was lighter too.
Geeze, judging sound by kg? Too much. Glad I'm USA.
I had no idea that amplifiers were sold by the kg. I can only tell you it weighs quite a few lbs. (your kg is close), but if you looked at market on us.ebay, it supports what I stated on "sold". A ragged SE-Axx will go for $800.
It is well rated in the Technics community, and does also have those awesome VU meters. The SE-A70 is similar to the SE-A5Mk2 but improved. The SE-A5 preceded both, so maybe reason it got superseded quickly and list prices rose. The seller on eBay.us now just listed higher after not getting his price last cycle.
It also is a fact that the market drives the demand, not weight.