thisisthenameofthewebsite asked: The spirit world and the middle plane between the physical world and the spirit world where Unalaq is and where wan and Vaatu had their battle are two different places. That plane is the bridge between humans and spirits. Since both entrances were closed to everyone except the avatar, the avatar took over the responsibility if being that bridge. Because that middle plane is not the spirit world the use of bending is still allow. Bending is not allowed in the spirit world.
Good explanation, ThisIsTheNameOfTheWebsite, but here are the facts of the matter:
If you meditate into the Spirit World, your body is left in the real world and therefore you cannot bend.
If you enter the Spirit World through a portal, your body is with you and you can bend.
The Avatar needs her body to enter the Avatar State.
The Spirit Portals are on the same plane as the rest of the Spirit World.