The vocal styles vary, because there are some death metal bands (primarily melodic death) who do some shriek-esque vocals.
And yeah, I suppose you kind of develop more of an ear for telling the difference between black and death metal. The difference is actually rather notable, once you know what you are listening for. Hell, after getting more into black metal, I've noticed some major black metal influences in some of Opeth's older work, especially in the drumming on April Ethereal.