I admit that I am one of those DK's that take a bit of damage. This is not because I am a noob or that I don't know tacts or such, but sometimes I am surprised by how much damage I take, especially on multi mobs. I am not even sure why sometimes until I get the beep telling me my health is low. If I hear it, I always move away to try and stop taking any damage.
However, I do always apologise to the healers and tell them that it is fine if I die
One of the reasons seems to have happened since patch 4.0.6. When the patch hit, I gained a few thousand dps (doint about 10-12k on mob and few thousand more on boss), but the amount of agro I generate seems to have gone way up. It has reached the point where I can pull single mobs off tanks without much effort.
Of course, if I see too much agro, I will stop dps, but sometimes by the time the tank has regained control, I will have taken some damage or perhaps died.
During one DM run, the tank and me even tried to work out why it was happening, but couldn't see what was going on.
Has got a bit better recently, so many it is just a gear thing.
Anyway, the point is that I fully accept that I am harder on healers then perhaps others, but I in no way blame them if I die
PS It is not an excuse, but it should be noted that I think Cata is much harder on Melee than Wrath was with a lot more AOE centred on boss damage.