You think the energy cost to transfer has dropped by 10 X in eight years? Why?

Seems reasonable to believe to me. The cost of a transfer is presumably calculated based on the base power cost of the transfer machinery, since I really doubt that a router or switch's power usage is linear with the amount of data it's transferring. The amount that an industrial router or switch (which is what 80-90% of the hops between you and Google are) has to have increased its bandwidth by around 10x over that time, and I doubt they have 10x'd their energy usage.