Yeah, which means you still have to crank the amp to get the power amp distortion. It works the same way if you are getting your distortion from the preamp section.
The preamp section of tube amps -- even great tube amps -- isn't all warm, glowy, dynamic, lucid, etc. These are all things from the power amp section. Preamp distortion, even on a good Marshall, usually has a sharper, sterile quality to it. Cranking the amp, working the power amp section and hitting the speaker hard, makes it sound good by the time it reaches your ears.
I just use clean tube amps like Fenders and Peaveys. I've never been extremely impressed with the distortion from the preamp section of a tube amp. That includes amps I've played by Matchless, Dr. Z, Marshall, Vox, Fender, etc.