I noticed this the other day while playing around with some different tanking specs. I attempted a Frost spec (I normally tank Heroics Unholy as the AE threat is really good) as I wanted to work in the 3% mitigation and the single target threat looks like it might be better.
To my surprise my threat vs the target dummy was TERRIBLE, and I think hit is largely to blame.
I noted my IT and Howling Blast both had a hard time connecting to the boss. This also caused a real problem in generating RP to use Frost strike as I was wasting GCs due to missing with these 2 "spells".
Any comments here from you Frost DKs? How's the threat?