@Tes yeux noirs,
I presume the poster would have to be the one to ask for an email address to be removed in a situation that isn't overtly spammy, but, as I said, I don't know if a moderator would (since I don't put my email in posts, thus have not asked them to do this myself). I have observed that they will leave them when they don't seem to be spam.
I think it is usually more due to the inexperience of the internet by the posters who do that.
As the once dummest person on the internet, I understand that.