I guess I don't see a crabs pin ability as a tanking ability, while I do see the Turtle's shell ability to be great for tanking. The Boar's Gore ability, while neat is also not what I would call a tanking ability. Croc's have ankle snap, and I am not sure when I would use that. All in all I think they did a good job upgrading the pets, but I would like to see them make all of the abilities a bit more useful. Then again, I have not played a hunter since Burning Crusade, so it may just be that I am not aware of all the great things they updated. You know the uninformed chap that doesn't see the big difference in what was yesteryear...
Also... uhm... I was sort of just trying to get a silly thread going.
That's because Pin is a kiting/PvP ability.
Different pets in the three trees are viable for other things than the exclusive purpose of the tree.
For example, I prefer a crab for BG and world PvP primarily because of Intervene. Charging a player you're kiting, Pinning them, then using an Intervene is pretty sweet.