Subtle or unsubtle, we have to know what we're trying to say. I already think Qui Gonn's death is different. Making him disappear will make him more similar to the other deaths. But we are probably not looking at this the same.
Here's how I understand things: Qui Gonn was killed. His spirit (seperate from the "secret of immortality" that he learns) goes to the great beyond where all spirits go. But rather than rest in that "other world," Qui Gonn's soul searched for the secret of how to return. He discovered it and used that secret to communicate with Yoda and teach him this trick. Yoda, in turn, taught Ben. Then, when the "chosen one" was redeemed and died -- his power and importance were enough for these others to "catch" him and for him to quickly learn this trick as well.
Anakin's body need not disappear any more than Qui Gonn's by this reckoning. The disappearing body is merely what happens when you consciously "do" this trick. Since niether Qui Gonn nor Anakin went through the meditative preparations, they did not "take" their body with them.
Since they are "immortal" only in the sense that they can now communicate with people on this side (apparently, in a limited way that works best with people in tune with the Force) -- the body is practically irrelevant. Ben didn't take his body to use it-- he just disappeared in a way that indicated his death may not be as complete as you would assume.
THIS, by the way, is the reason I love Vader's silence as he pokes around Ben's robes with his foot. What should he say? He's never seen THIS before. He presumes he's killed Obi Wan, but then again something's not right. Ben had warned him not to strike Ben down. His reaction is the way a bad-ass says "what the hell was that?" Making him say "It is finished" makes Vader a sap who can't see that something odd just happened. He's cut down dozens of Jedi and none of THEM disappeared. Why is this one different, he should wonder. If he doesn't wonder, then he's a fool. I prefer a Vader who isn't a fool. I prefer a bad-ass.