I thought they repealed those rules once they established replay. The point of the rules was to help the officials avoid needing to make split-second calls. If there was "enough" time left when the play started and the shooter seemed to go through the motions quickly, without hesitating, then the officials would guess (barring other information) that the shot was good.
With replay, I can't see what impact those rules would have. If the clock starts at 0.3 or even 0.2, but the replay clearly shows the shot leaving in time (and the clock starting correctly), then what is there to dispute? Similarly, if the clock reads 0.5 and everything goes smoothly, but for some reason the player is still holding the ball at zero, then there's no shot.
I bet you could get rid of the ball really quickly if you wanted to. Imagine that you're catching the proverbial hot potato. If you are young (before reaction times lengthen), your hands won't be in contact with it for as much as 0.4 seconds, especially if you can see it coming and know that you're going to have to get rid of it.
There's one other point in this case that may have helped. The official scorer is not supposed to start the clock until someone in bounds touches the ball, and he is also not supposed to anticipate that the ball will be touched by someone -- he's supposed to wait until real contact. Fisher had his back to the scorer's table and there were a lot of big people in the way, so it may have taken the smallest fraction of a second more for the scorer to see what he needed to see.
It's arbitrary anyway. It reminds me of the NFL, when the officials use guesswork to spot the ball in the general vicinity of where it should go, and then there's this big elaborate precise measurement to see whether the ball carrier earned a first down. Did Duncan's shot really go through the net at 0.4? For that matter, did the clock on the Spurs' last possession start at exactly the right time? Probably not.
So there will always be an element of randomness (or, if you prefer, serendipity) when a game is decided on a buzzer-beater. As usual, that randomness favors the Lakers. No one should be surprised.