I don't see what the problem is with that advertising- they only said that tube amps SOUND louder than equivalently rated SS amps, which in my experience can often be the case. Lots of factors contribute- compression and added harmonic content in the midrange being the big ones I think, both of which make tube amps sound louder especially when pushed. You can emulate those factors with a SS amp too- the Walkabout is a great example, and that amp to me cuts through a mix better than any other 300 watt SS amp I've owned if you push the Gain and Volume a bit.
An uber-powerful solid state amp can pummel most tube amps in big uncompressed low-end reproduction, but those aren't the frequencies we hear the most efficiently and can get lost in a mix whereas the pumped up midrange of a driven tube amp cuts right through. Soloed through my 610 cab I can almost make myself sick with the amount of low end my DB750 puts out without a sweat and give myself ear fatigue at relatively moderate Master settings, but in a band mix my 250 watt Prodigy actually sounds louder to my whole band (and this is with the Mids on the Aguilar bumped significantly). I had the same experience comparing my old 400+ and SVT to an Ampeg SVT-4Pro through an 810.
So it is true that a watt always equals a watt from a mechanical perspective (which means a high powered amp will always pummel a lower powered amp through an inefficient or heavily scooped speaker), but through a fairly efficient speaker a tube amp CAN sound louder than an amp several times it's power rating (but only by sounding and responding noticeably different!).
