As I just answered in that question, emails for Q/A/C responses are decided by the user (the "Email me if..." checkbox).
With notifications it probably does make sense to untick that by default as they'll see notices on the site.
Perhaps it may also make sense to have a page listing a user's email notifications so they can mass unsubscribe to them. (Currently the only way is editing every post, unticking the box, then saving.)
What do you think?