I think the weights are just a number someone pulled out of their tailpipe.

I just finished assembly of a Great Planes Big Stik 60 ARF. Advertised weight is 6.5 pounds. My plane weighs 7.5 pounds.

Engine OS 91 Surpass II. Weighs 24.2 compared to 23.6 for a 61FX (OS specs from manual, with muffler)
Converted to tail dragger. Added plywood gear mounting plate and tri-stock, no idea what it weighs. Substiututed tail gear for nose gear, probably saved weight there.
Tru-Turn spinner versus nylon spinner.
4 Hitec HS425BB Servos
1 Hitec HS322 Servo
4 AA cell 1650mah nimh battery pack
Hitec Supreme receiver

I have no idea where it gained the pound.