Not going to cry here just yet. But it seems like the DK in question (Deviumm) is using plague strike? As frost? Probably has Glyph of Disease im betting. And he's subspecced into unholy. The damage that necrosis and blood caked blade is doing is pretty pathetic when i look at the numbers.
You get x2 as many rime procs DW since the offhand weapon hit counts towards its own chance to proc Howling Blast. I never had a problem keeping my diseases up with howling blast glyphed with rime before. The DPS should be very impressive to say the least.