I think it's most likely the fact that it was because y'all are forgetting one vital piece of the story: Harry's body was inhabited by two souls.
"You were the seventh Horcrux, Harry, the Horcrux he never meant to make."
Both Voldemort's Horcruxed soul and Harry's were within his body when the curse was cast. Harry originally withstood the Killing Curse once due to the sacrifice of his mother, thus causing the curse to rebound upon Voldemort, killing him and forcing him to find the other portions of his soul.
When Harry went forward to allow himself to die, Dumbledore explains to Harry why his soul survived.
"Precisely!" said Dumbledore. "He took your blood and rebuilt his living body with it! Your blood in his veins, Harry, Lily's protection inside both of you! He tethered you to life while he lives!"
With Harry living for as long as Voldemort is alive, it would stand to reason that Voldemort's killing curse would not affect him but rather the OTHER unprotected soul within him: Voldemort's last Horcrux.
With this last bit of perversion gone from Harry's soul, his mother's protection is no longer perverted by the corrupt soul of Voldemort. This purified enchantment laid upon Harry by his mother allows him to no longer fear the magic of Voldemort. I say this because Dumbledore explains the connection between the two:
"He took into his body a tiny part of the enchantment your mother laid upon you when she died for you. His body keeps her sacrifice alive, and while that enchantment survives, so do you..."
I make this claim because the only major difference between Voldemort and Harry in Goblet of Fire (Where Voldemort successfully used the Cruciatus Curse on him) and this last scene, is that Voldemort's soul is no longer within Harry. Voldemort was able to torture Harry because his Horcrux was latched on to Harry, weakening the enchantment his mother laid upon him. With this contaminant gone, Harry now had the full undiluted protection of his mother's sacrifice (at least from Voldemort).
On a quick aside: I would assume that he is still susceptible to the magic of others but no others cast magic at him for the rest of the book.
So, to wrap this all up:
Harry didn't feel the Cruciatus Curse cast by Voldemort because he was, once again, fully under the protection of his mother's enchantment. An enchantment which was being sustained by some of Harry's blood within Voldemort.