[tpeo]

I wouldn't say that's the case for most songs, but rather only for simple melodies. But yeah, a graver voice would sound better in most cases.

Consider the beggining of Bach's "Little" Fugue in G Minor (BWV 578), where the subject of the fugue is first introduced by a soprano voice and then repeated by an alto voice, while the soprano voice does the coutersubject. I'd say that, played in isolation, the melody sounds better when sung by the alto voice. But lowering the whole Fugue by a half-step wouldn't make it much better.

[zubat]

With respect to recorded music it tends to be the opposite: if you pitch up a track then the rhythm feels tighter and the vocals more steady, because the differences between the intent and the performance are relatively smaller. Hence an old studio trick dating at least back to the Chipmunks was to record in a lower key. Listener discrimination seems relatively less important in practice, on the other hand.