Though I can't say for sure why they don't exist, as a web developer myself I can take a pretty good educated guess. The editor that is being used in the discussions is different than that of the Blog feature page, or even the wiki. The logic behind that is that discussions tend to be more of a "casual" conversation amongst peers, while a blog is more of a full blown article that would require some more intense formatting. As well, the wiki would also need such tools, to articulate whatever topic of learning that is being conveyed properly. So, the next underlying question would be why not just add all of the tools to the editor anyways... right? That's simple; it takes resources from the server to keep loading all of those tools onto the page over and over again, and as well slows down the load time of the page. Since a full list of tools really isn't needed as a general rule, I'll guess that's why they've been left out.
