Are you sure they're not just playing to a different scale?

I'll agree that "in tune" is a whole lot easier to listen to than someone who "plays in the cracks," but it should be remembered that "in tune" must be relative to a specific scale. Orchestras and jazz have pretty much gone to equitempered, and that's what we're all used to. Barbershop, solo fiddle, and maybe unaccompanied voice or trombone solos, are about the only places left where "just" tuning is still heard much. "Other world" music uses scales that sometimes set my teeth on edge.

The use of deep/complex chords in jazz, and in "classical orchestral" work, makes it pretty much necessary to be "in tune" in an agreed on scale there; but lots of old (especially folk) tunes probably were not "made for" chord backup and "strictly in tune" rendition.

I haven't heard enough of the artists cited to offer comment on their specific playing; but "classical training" can be a curse of sorts, if it gets you too intolerant of a little "bend" in the scales - assuming of course that what's being played is appropriate to the music.

John