Anybody who cares enough about you would already know it's your birthday. The only purpose of posting it on a public forum is to receive the well-wishing of people you more likely than not don't know. This is for attention.
I don't mean to sound rude or disrespectful, but weren't you the one who posted that topic about your friend HPRC dying? That in itself could be considered an act for attention.
Sure, it's not entirely necessary to state that it's your birthday on an internet forum, but why not do it anyways? What's wrong with having a few other people say "happy birthday" to you?
I can say the same thing for the topic on HPRC. It wasn't entirely necessary to post that topic, but what's wrong with having people on an internet forum comfort you?
