Yes, links like those are referral links that can be used to get a 20% discount on any item in d2d website. Seems that there is no time limitation or pre-order restrictions for this code.
People have been posting them all over the official forums, I got a few other that serve for the exact same purpose: http://direct2drive.tellapal.com/a/clk/5DfCl
So how it works, you go to that link, copy that code while doing the check out for your item, and you get 20% off, it also seems that the person that provided that code gets some sort of benefit from it.
There was another code going on last weekend, at D2D, wet kitty, but seemed that this code wasn't meant to be used to pre-orders, tho some people still used it and they said it worked, I personally didn't try it, I used the code I posted here.
Dreadblade just make sure you copy the long code from any of the referral links while doing the check out, it should ask you if you have any promotional code, before you add your credit card info etc.