Well for a start EJ is not always the best resource for everything However on the first post of the DK tanking thread they write;
Later their THread author says
The fact is - A Death Knight tank who has the ability to manage the numerous cooldowns properly, time death strikes optimally, and use their self healing at the correct times - you will find yourself able to do many things other classes cannot. Sure, you are going to be 'spikey' at times, but that is somewhat the premise of the class itself. A Death Knight excels at single target tanking, and that is it's niche in the current tanking scheme (which I am a fan of greatly). You are going to take more dmg, but you are also going to heal yourself for a ton more and be able to save a lot of situations where other tanks wouldn't.
Further on, around page 5 somone posts a little Table regarding DS sims
If you are just standing there face tanking bosses with shit class management, sure, you're going to be getting wrecked whereas on any block tank class (warr / pally) you will still have your mitigation working for you because of how blocking works. Even on a druid, getting SD to proc off of crits is something you don't really have to time, but rather just allow to happen since it is based on RNG (crit) while doing dmg to the boss. These things just aren't the case with a Death Knight because of how much gain and penalty is put on the timing of your DS and usage of your arsenal of cds.
So, my sim confirms the conventional wisdom - timely death striking is more important at high damage levels than keeping runes cycling, dodge > mastery for physical damage fights, mastery > dodge as more magic damage appears, though in both cases the relative increase in value is somewhat marginal. For lower damage levels, DS on cooldown makes more sense as it is more difficult to get far beyond the 7% max health DS minimum