I've wondered about this myself, submissions without hyphens seem to have them added often (by admins no less, for instance
here.) I also recall some album where the only edits listed were the hyphen being removed, and then another edit dated a year after the first restoring the hyphen (both by admins, actually.) So maybe hyphenating is the unspoken policy? I'm certainly not opposed to it, I like to preserve information as it's given by the artist/label but in this case it's nice to keep things uniform.