Tube Watts vs. Solid State Watts - Any credence?


I've heard numerous times that Tube watts are not the same as Solid State watts when it comes to amps running speakers. For example, a 70 watt tube amp provides more power than a 140 watt solid state amp. Is there any credence to this or just sales talk and misguided listeners? If so, how could this be? One reason I ask is a lot of speakers recommend 50 - 300 watts of amplification but many stores have 35 watt tube amps or 50 watts tube amps running them. More power is usually better to run speakers, so why am I always hearing this stuff about a tube watt is greater than a solid state watt?
djfst
And without knowing the, uh, drum roll please, efficiency of the speakers.
How does a large power transformer affect high frequencies?

Output transformer, maybe...
The large magnetic field produced by large transformers cannot be good for any frequency, high, low, what have you.
Geez, guess I'll have to send both of my 62lb output transformers back, then...