Every other class had their taunt changed and it has me worried a little.
Sky is falling theory: Vengeance is going away, or will be nerfed so severely it might as well be gone.
Probably theory: The change is so when a second tank taunts, he can taunt again 8 secs later for increased threat generation preventing 1st tank from taking it right back.
Just find it interesting they needed to make a change at all.