I'm not the OP, and I don't use ISBoxer (yet), but I can tell you that the 4 Blood DKs could be for BOTH PvE and PvP.

I'm working on 4 DKs myself, currently lvl 70. As I did Frost DK + 4 Ret pallys in Wrath, I rolled them with the specific goal of being Frost for chaining AoE CCs and slowing mass targets with Howling Blast. Not sure what I was doing wrong this time around, but after using Blood from lvl 64 to 69 and then trying to go back to Frost once I reached HB, I found that neither the consistent damage nor the useful CC was what I expected it to be.

I'm back to Blood now and loving it. Pwning in BGs easily even though I'm only 70 in the 70-74 bracket, and UK runs are going so smoothly that the random healers are the ones asking me for the requeue.

I'll stop with the hijack now and get my own thread going on this later, but I wanted to help clear up the point of Blood spec immediately.