They are not purely cosmetic, but the Touch Bar models have 'more' cosmetic speaker cutouts, if you will...
On the nTB 13" there are clear cutouts for the sound to pass through, and there are no air vents, so all the sound passes through these holes. Picture:
On the TB models the bulk of the sound comes through the air vents on the sides, but there are still some holes on the bottom of the grille that the highs go through. It sounds noticeably worse if you cover them. Picture:
So the real story here is the presence and absence of air vents - which impacts the location of the speakers.
Both use the speaker holes: the nTB exclusively, and the Touch Bar partially.
(Images courtesy iFixit.)