People like Micheal and Walt didn't change on The Island and so don't need to remember in the same way the others did. Micheal said it himself, he's stuck roaming around The Island until he can make peace with himself.
They changed. Walt pretty much came of age on the Island, developed his psychic powers (for all the good it did plot-wise), and befriended Locke. Michael really became a father for the first time, befriended Jin, and even answered the call to go back to the Island. Like I said, they had as much reason to be there as Boone and Shannon, really. And also like I said, if it's limbo and time is elastic - everyone in the group should hit the point where they can move on together at the same time.
dont wanna see any spin-offs, games, etc. it ended. it's over. as much as i want to see more of these characters i just dont think i need any more LOST.
And in regards to the church scene at the end, we were seeing everyone through Jack's eyes. How HE remembered them. That would be how Jack would see them in the afterlife, etc. Aaron may have lived to be 75 years old, but Jack knows Aaron as a baby. Hence, that is how Jack would view Aaron.
k, I like this explanation.