Mr. Sandman is definitely pop (or at least it was) but if people like it and are still singing it, maybe its moved into the folk realm. My mother used to sing it but then she sang songs from Mahalia Jackson and Patsy Cline, too. I sang it to my 27 year old daughter (she had never heard it before) and after she stopped rolling her eyes, she asked me to write down the lyrics. Who knows? Maybe its for the fun of it or maybe its just plain funny.