The difference is that we're queued for the role we're using. You do know Blizz isn't that specific right? For example, in Heroics, there may be two items of each slot that a Hunter could use. Yes, one may be Mastery (better for BM) and another may be Crit (better for Survival), but there are still only two. However, that also means there are two Resto items for each slot and two Elemental items for each slot. See the difference?
There's not 2 pieces for elemental and 2 pieces for resto, though. Most slots have 2 choices of int mail (shared between both) with some slots having 1 choice, and 1 slot having 3 choices.
Elemental uses spirit so blizzard doesn't have to itemize resto gear and elemental gear independently. They basically itemize one type of gear, int mail and call it good. Often giving choices on some slots for spirit or not so shamans don't have a silly amount of hit.