I guess the extreme example of an SG with noticeable neck dive would be the unpainted, thin bodied swamp ash or light mahogany, set neck design and heavy tuners. The factory Gibson SG is very thin. Lots of those SG copies and knock-offs might have thicker bodies and covered in some poly paint and /or clear coating. I've stripped as much as 1 lb of finish alone from some factory made Ibanez etc. brands. Lots of SG copies also feature bolt-on necks which add a bit more weight (neck plate and screws) to the body. One poster mentioned that his factory SG weighs 10 lbs, that's HUGE considering SG's in general. Chalk it down to the frequency in wood density within a species, I've seen ash almost as light weight as balsa and as heavy as oak. Mahogany has quite a density range as well. I guess every little bit counts eg. TOM w/ tailpiece vs. wraparound bridge. Or presence of a Bigsby.