Well, by your logic, singing is a ridiculous form of communication too, since nobody's going to walk up to you and try to communicate by song.
I'd be pretty fucking disturbed if I went up to the counter at the supermarket and they either sung or growled "how are you, do you need a bag for that?" at me. Doesn't make it ridiculous in context though.
I honestly don't get the fuss about the growls, to be honest. I mean, it's like being pissed off because somebody sings in the key of A or whatever. So what?