To clarify, we're not comparing the different tones coming from the amps, we're talking about warmth of the preamp tone.
From my limited knowledge with only a few Mesa amps, technically this warmth might be a result of natural tube compression (but two amps with the same tubes don't have the same warmth), a specific circuit design, components, or all or none, I don't know, but I know what he's talking about. I just describe it as "lots of natural compression".
My old Triaxis and 50:50 had it (Petrucci Live tone sold me). Same tubes in the Roadster and the warmth isn't there. I'm going to find out if the Lone Star has it. I still like the Roadstar, but I miss that. The Triaxis Green (Mark I) and Red (Recto for Mine) had it.
It could very well be that this amount of amp compression is only available in certain models.
EDIT: If you haven't, try to find an opportunity to experience the warmth we're talking about, its magical.