Except so many of them are culturally specific, like the horn emoji on the front page has roots in postal systems (both in Japan and Europe). This page doesn't tell you that. Even this random website does a better job of giving context: http://emojipedia.org/postal-horn/

That essay has a good grasp of why we want unicode, but completely missed the point of why we want emoticons. If I send an image to someone, I don't want it to be rendered in an unpredictable way based on their unknown system and font choices. I need to know that they see what I intended to send.

Everyone would be happier if they were embedded images; that's what we all want. They're shoehorned into unicode instead because that makes it technically easier to send them in text messages, not because they're textual objects.