Funny enough, this came up on another thread just the other day and Jeremy pointed out that while email and messages are options, individual users can disable reception of those. So to add to what knudfl has written, it may also be a situation where they disable email and message reception.
http://www.linuxquestions.org/questi...4/#post5296472
I should also add that in the LQ Rules, it states that email addresses are not desired/acceptable in thread postings and while they may get in there originally, they'll likely get removed once a moderator becomes aware that someone has posted an email.