Why are so many GameCenter All Time high scores 9,223,....?
If you search "9223372036854775807", you'll find this article on Wikipedia. The important thing to note is this line:
The number 9,223,372,036,854,775,807, equivalent to the hexadecimal value 7FFF,FFFF,FFFF,FFFF16, is the maximum value for a 64-bit signed integer in computing.
So the reason why so many high scores are 9,223,372,036,854,775,807 is because this is literally the highest possible integer number that can be stored, even if it isn't achievable in-game. These scores are most likely hacked, but this is why that particular number is chosen.