Was it strictly necessary that at the end of The Big Bang Amy had to remember the Doctor to restore him? Could River, Donna, Martha, Rose or any other previous companion have brought him back, had they recalled him?
Amy had always been closely tied to the cracks in the Universe. The entirety of the Pandorica trap was built from her memories, and her memories (in part) were used to rebuild the Universe.
She had to remember the TARDIS and the Doctor because, lacking those memories, he could not have been reconstructed. Her brain was the only one used in the recreation of the Universe, not those of any other companions.
As the Doctor said, she grew up with the crack in her wall. During her formative years, information from the whole Universe was pouring into her. Amelia Pond, the girl with the storybook name, is the only one who could have brought him back.
For one thing, the Doctor planted the idea in Amy's head, and not in anyone else's (in his "we're all just stories" speech, where he very carefully associated "old, new, borrowed, and blue" with the TARDIS). So even if it wasn't necessary, it was a lot more likely that she'd remember him than anyone else.
I don't know if there's any more to it than that, but here's some speculation: