Internally, every drive is able to read the leadin / first pregap,
but not all are able to deliver its content directly in raw mode.
The main purpose of that overreading feature probably is to get all the audio data without missing samples when correcting the offset (keyword is EAC).
In reality the drive doesn't have to overread, at all. But due to its introduced offset, it "thinks" so. Actually this is complete nonsense and could be prevented if the manufacturers would finally set the offset to just being 0. I'm sure that if a software is able to correct it, a firmware should be able to do this even more.