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?it's just sales talk & misguided listeners. No credence to this statement. As Mapman & many others before have written: a watt is a watt tube or solid-state.
Ralph Karsten of Atma-sphere has written a paper on power amplifier paradigms:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php