Just cuz you can, doesn't mean you HAVE TO.

This might seem obvious to some (maybe most) people, but I figured I would put this little information out there anyway.

I'm a paladin. I can wear plate. However, that doesn't mean I HAVE TO wear plate!

Currently, I am wearing 2 pieces of mail gear (because every boss we kill in Naxx flat out refuses to drop plate healing gear). The boots and legs are great for healers, whether they normally wear mail or not. My group having no shamans in it, I immediately snatched these up.

This can be true for hunters too. While Blizzard has done much better at putting intellect on the mail hunter/shaman gear, sometimes a piece of leather is much better than the piece of mail that you are wearing. This may not be true in the end game, but especially while leveling it can be.

Now, Paladins are capable to wearing leather and cloth too, but I personally don't like to. With the spellpower changes, a piece of cloth is going to be worthwhile for any caster, and I'll leave those to my mages or priests who need upgrades first.

Bottom line: wear the gear that makes you a better player and upgrades your gear. Don't get hung up on the "plate, leather, mail, cloth" classification (to an extent) and focus on the stats you need.