Surely the revs drop when you lift off the clutch? :S
The only reason this is a tiny inconvenience to me is on the rare occasions when cruising i poke 2nd a bit n then put it in 4th. Then I give it a tiny bit of time to drop a bit.
Normal driving it shouldn't be an issue though...
It's all due to inertia .... heavy flywheel or crank and such take more time to slow down (hold more energy)...also take more power/energy to speed up.
I don't think it has anything to do with wire-driven or drive-by-wire systems.