I mean maybe the others werent strong enough, or in touch enough...I cant be sure now cause all the other info has biased me, but I think my thought on it was based on the dissappearing thing. I never saw it as Obi-Wan got cut in half and vanished. I saw it that he vanished into the force of his own will before he was cut down. Same with Yoda, he became one with the force before/as he died. I always figured Anakin's body was in the suit but that being burned 'set him free' so to speak hence his appearing at the end.
Its one of those things that was never a problem until Lucas made it a problem by addressing it (or trying to address it)
-Darth Simon