"tube watts" versus "solid state watts"


I'm sure you, like me, have seen it written more than once that brand X tube amplifier, rated at 30WPC, sounded more powerful / more authoritative than brand Y solid state amplifier, also rated at 30WPC. Or that brand Z tube amp, only rated at 15W, was comfortably able to drive brand A speakers, because those 15 were tube watts and therefore up to the job. Heck, I think I've even heard the phenomenon with my own ears.

My question is: is there any basis in electrical engineering for this effect? Can we say scientifically what's going on here?
128x128twoleftears
Arahl...Some SS amps have circuitry which detects when clipping is imminent, and limit gain so as to behave very much like a tube amp when overdriven. Also, consider that SS amps are, for any price point, much more powerful than tube amps, so that when the tube amp is clipping the SS amp is not.
A Watt is a Watt is a Watt.
An inch is an inch is an inch.
Despite logic and reason, measurements seem to be gathered by perception.
Tubes are men.
Transistors are women..