Tube amps tend to produce less unpleaseant-sounding higher-order odd harmonics than solid state and potentially more even lower-order harmonics which are pleasing to the ear.
Piano overtones are stretched over harmonics and beat with them. On overly warm gear piano sounds like out of tune. I believe that we got so used to home gear that produce some distortions, that perfect reproduction of life event, that you enjoyed, at home sounds wrong - sterile, analytical etc. Distortions make sound more dynamic and often we want them for this reason. I suspect that it is because of compression. We try to get back dynamics of the real performance. Either way - there is no right or wrong, just a matter of taste. I'm in the accurate camp, choosing accurate timbre over false dynamics.
