The astral plane is also called the metaphysical world and the spiritaul world. It is a diffrent plane of existance than our physical plane. Astral things may walk around on the physical that doesnt mean the physical is the astral plane.
When with my spirit body, in the spirit world (not the physical world) walk around that is astral projection
I see the astral plane as more of a generic term of not being in your physical body, and believe there are different realms within the plane you can enter and that's where different creatures live. There, I think that makes more sense :P
I think that we share the astral plane with these spirits but they like us have their own realm. Just like all the other kinds of spirits, and just like its very hard to go to their realm for us, its hard for them to so we see them in the bridge we call the astral plane.
I was discussing these eariler with a friend of mine. Not "fairies" but nature spirits in general, and that applies to many many "types". Before there were angels, there were nature spirits, and some believe that angels and "demons" are merely benevolent and manevolent nature spirits. However, they are closer to the physical world than your average spirit. Like psychopomps, deities and our own out of body experiences, they are seen to be inbetween.
My own theory on this is that nature spirits are special spirits residing within physical aspects of nature. Because they are semi-divine (yes many believe this) they have a higher level of consciousness and a born magick. When they interact with us, it is likened to when we project. I believe most of their activity is through projection while their physical form, be it a tree, a body of water, or a crystal, sits motionless. This is my own idea as to why they can influence, physically manipulate objects, and even manifest seemly effortlessly. I believe their magick is on our level but their wisdom is far greater.
i don't deal with faeries, one of my coven makes do though. we've talked with faeries once or twice, whenever i see them i see a purple orb out of the corner of my eye, i've seen orbs of spirits before, but never a purple orb. i don't know the in's and out's of it, but i think it's earth based and you're calling upon creatures with earth based power [for lack of a better word]
same goes with dragons, vampires, and werewolves [not real on this plane unless we're talking about psi vampires blah-blah-blah] people incorporate these beings into their craft to gain strength from them. where the problem lies is most people grew up with faerie tales/movies/tv telling them grand stories about these beings. so when people start following a pagan path, they'll think dragons are giant fire breathing monsters who eat virgins, vampires suck the blood of their victims turning them into vampires, werewolves change under the full moon, and faeries are tinkerbell like.
in the physical, these things aren't real. most people though don't want to separate fact from fiction because fiction is much better than fact. in most situations, that's how all these spells and false claims come about. personally, i love faerie tales and mythology, but they're just stories. [course if they were proven to be true that would be neat, but i'm 99.99% sure they are not.]