Replays are literally the game starting a new race but with automated control inputs it recorded when you actually raced. In other words, the replay doesn't record video, it records your controller inputs (as well as the locations, etc of other cars) and then simply plays the race again from a different camera angle and using your recorded inputs.
Sometimes if there is some bad code or a bug somewhere it can lead to the replay looking nothing like the original race, such as cars turning off into gravel traps, etc.
So, it sounds to me like either the PS3 skipped a bit or you managed to find a piece of code or track position that effects the recording of the input. Or you're just forgetting what a good driver you are

I doubt it records point positions because its far easier to record the inputs, which you can record into double float lengths easily. There may have been some error loss somewhere though, which would cause the PS3 to skip the number a bit because of rounding, but this wouldn't make it look tidier

it would cause it to be jumpy and cause further inaccuracies down the line...enter chaos theory.