The problem with this "explanation" is that the application's effort to use vertex buffers is significantly higher than the effort to use immediate mode.

A hardware implementation of IM (like the one in Silicon Graphics machines) would probably bring much higher energy efficiency than carefully packing up VBOs with software. Even when there's no hardware implementation, the packing up can be equally well performed by a driver, thus just shifting the energy consumption around, not increasing it.

Thus, immediate mode is actually at worst just as efficient as VBs for small vertex counts or dynamic objects, and at best allows hardware acceleration where there is none with VBs.

Yeah, that might be pretty cool. But then you have to calibrate it.