I am currently rereading all the books, and a previously overlooked yet certainly key distinction keeps coming up: the reason for Harry's survival vs. the reason for Voldemort's loss of power.
In the first chapter of COS, we read that:
"Harry had escaped with his lightning scar, and somehow--nobody understood why--Voldemort's powers had been destroyed the instant he had failed to kill Harry" (COS, 4, hardcover).
Much later in the book, when Harry encounters Voldemort's diary-held memory, he reiterates:
"No one knows why you lost your powers when you attacked me...But I know why you couldn't kill me. Because my mother died to save me" (COS, 316, hardcover).
It is there established that Harry survived the Killing Curse due to his mother's sacrificial protection. Common sense would dictate that the rebound of this Killing Curse was what left Voldemort a shell of his former self and made him lose his powers. However, that is clearly not the entire case, as we keep hearing "no one knows why you lost your powers" from a person that knows why he, himself, survived.
Finally, in DH, we get some clarity from Dumbledore about a possible contributing factor: the Horcruxes.
"He had rendered his soul so unstable that it broke apart when he committed those acts of unspeakable evil" (DH, 592, hardcover).
And from JKR herself:
"It was just that [Voldemort] had destabilized his soul so much that it split when he was hit by the backfiring curse" (Pottercast Interview, 2007).
Thus, it is at least implied if not outright proven that Voldemort's loss of power had something to do with more than simply the rebound, but also the degree of destabilization his soul had experienced to this point.
My related questions are therefore:
Would Voldemort have lost his powers if he hadn't previously made 5 horcruxes? In other words, would a rebounded Killing Curse not necessarily strip the culprit of his/her powers?
Would it have been different if he had only made 1 Horcrux (not "so unstable")?
Finally, am I looking into this way too much? Did Harry simply fail to equate the causes of his survival and Voldemort's downfall, and did Voldemort lose his powers simply because of the rebound?