Quoted from EJ at 3:00 AM on 6/2/2011
"Stats and gems
[...]
How to gem is not yet conclusive, however there is a strong argument developing that you should bias avoidance and mastery rather than stamina.
[...]
Mastery as a stat does not increase your classic EH [Effective Health], but increases your survival, as does avoidance which will be a more interesting stat choice in Cat than it was in WotLK."
The post was updated for 4.1 on 4/27/2011
Stam only increases your Death Strike Healing if you are at the floor of damage taken. Dont forget that death strike goes off of your damage taken in the preceeding few seconds OR a % of your hp, whichever is greater. Sure, rune tap scales but how often do you use that? Surely not nearly as much as Death Strike. The people doing the theorycrafting are worrying about HEROIC content now, not normal content and heroic content is all about survivability and getting hit like a truck. You're getting hit so hard that your DS healing will almost never be based off of your max HP. Furthermore, great DK's are able to line up DS's to act as mini-CD's for damage bursts. They get hit a bit harder than other tanks but when it comes time for them to not die, a DK has all the tools necessary to guarantee his or her own survival. Blood shield plays a huge part into this niche so mastery is usually the preferred way to go for heroic content right now when it comes to DK's
rune tap is a 30 second cd (will of the necropolis resets this cd whenever the dk is brought below 30%), vampiric blood is a 1 minute cd... not to mention blood dk mastery is based off of death strike heals which means that more stamina indirectly means more mastery
i'm just going off experience as a healer healing a blood dk. we're able to 2 heal heroic conclave of the winds in 10 man because agroshibs doesn't need a healer because he can heal himself indefinitely, we were able to kill sinestra because agroshibs doesn't need healing at all because death strike spams pretty much get him topped, he's able to tank 2 bosses at once for heroic omnotron and not die, he's able to tank onyxia in p1 and nef for p3 without a healer... etc...
i only have a level 80 dk and haven't played him since wotlk, but agroshibs tanks so well with them with average gear that i'd think he knows what he's doing