Why run speed?
Simple. The more quickly you get to where you need to be, the more quickly you can cast that heal spell.
I'm sure people can manage without it, but it's not like you cannot manage without 7mp5 or 12 crit.
For those who elect to spec into ret, PoJ should be a no brainer. For those of us who spec into protection, there is only one place we can upgrade our movement rate and that's with tuskarr's.
I can get 7mp5 or 12 crit lots of places. I can't get run speed lots of places.