Hi Rick,
Judging from pictures and specs, the YPG-625 and DGX-620 are the same keyboard.
My Acrobat Reader (v. 7.0) downloaded the Japanese font automatically. There was written '8.3kg' under DGX-220 and '25.5kg' under the DGX-620. Perhaps that is the weight including the bench:
25.5kg (japanese) - 18kg (musiciansbuy) = 7.5kg

Moreover, according to my DGX-305/505 manual, the DGX-505 bench weights 7.5kg.

Regards,
George