[ben7799]

There are certainly guitarists who can play simultaneous melodies.

If you're limiting to a 6 string guitar the distance between the two melodies would be limited compared to a piano but guitars don't have to be limited to 6 strings.

Classical guitar is full of this kind of thing.

Having taken piano lessons but being more into guitar I think the thing is almost all people who play piano are introduced to this and it is a core concept in far more piano music than guitar music. But it is not impossible on guitar, and many works for piano that get adapted to guitar require the player to do so.

E.x. there are plenty of players who have studied and played the Well Tempered Clavier on guitar.