problems with the dkFollow

I guess that I'm just having problems understanding the place of a death knight. I get that they can dps or tank much like druids, pallys or warriors. What I don't understand is where their threat comes from. Like with pallys their threat comes from getting slapped around as well as the holy damage, and then with warriors and druids it's all about the white damage, so what's the threat producer for death knights?

I ask because looking at some of the talent specs for tanking in the frost tree, it's kind of a mixed bag it seems. Some people don't take talents that help you to increase your +hit abilities, and some people max out their, well what I would call their magical abilities over their +hit abilities. Am I just making this harder than I need to?