User blog comment:Epakrios/Plot holes/@comment-6637171-20140119112655/@comment-1509826-20140119205629

Well, considering Heaven is pretty much subject to what ever the angels want it to be, it makes sense they can take any apperance what ever the want there. Zachariah presumably just took his vessels form, to make it easier for Sam and Dean. As for Rachel and Naomi, its possible Naomi was already in her vessel. Or it was mearly viewers benefits, as the true forms of angels is to extreme to show (or afford) sort of like in films were the foriegners all talk english, we know there meant to be talking some other languaged, its just the viewers benefit.

As for Crowley, assuming Sam's mind is much like an obscure realm, he took that form just to make it easier for Sam. If he took a generic demon form (which is apparantly, unatarually ugly) it would make it more difficult for him and he only had a limtied time.