There seems to be a good amount of confusion here. There’s a couple of points I think are worth reiterating.
This isn’t censorship and links to the DM aren’t “banned” or “blocked” or any such thing. You can link to the comic in question perfectly readily, there’s a URL in the OP doing exactly that.
The forum has a text filter which could easily be utilised to block the name of the paper, replace it with “Waily Fail” and send all the URLs to dev/nul, in much the same way as it does currently with phrases like ****, ****, ****ing ****stick, and Richard Stilgoe. As the more observant of you will have noticed, STW doesn’t do this.
Rather, when you follow a link to the DM, you get a confirmation as to where you’re about to be directed to, and are given the option to change your mind. It’s a bit like a NSFW warning, you’re being asked “are you sure?”
Should you decide that actually, or reflection, yes you do want to contribute to the DM’s hit count, you can do so using the link provided, with joy in your heart, a spring in your step, and gay abandon(*). The only difference being, the link gets a nofollow tag attached with it, and STW kills a kitten.
As for the reason this is done, well, there’s an explanation on the landing page, and also I expect a few of the comments here aren’t too far off the mark in relation to nefarious SEO tactics. Plus, let’s not forget, it’s bastard funny.
(* – so long as you don’t want to marry one, they don’t like that sort of thing.)