In fact, it will be extremely common to run into several Blood DKs and find out that none of them use the same talent build, as they swap talents around as needed for their raid. This guide will cover 3 sample Blood DK builds, but in reality, after you have understood what each ...
Some tanks just have poor threat modifiers in general leading you to spec a weird way to exclude them, and others are designed so poorly that playing the class just isn't fun (WoTLK DK tanks aren't fun to play when threat actually matters). On live it generally isn't a thing...