Also, the 10% threat-reduction isn't a problem at all in the given content. It might become (as it was on Lich King), but it isn't now. The ability also works for non-tanking people as well as mentioned above.
Safeguard and Piercing Howl are two interesting "tools" Prot. Warriors can and in my opinion should bring to the ball game. It's not needed for every fight but useful for quite a few.