Saying that it should be repeatable every time in a pressure situation was a bit much on my part. But it should be repeatable to be statistically significant, meaning that someone does it more often (or less often) than what would happen by random chance.
As for the statement that I've bolded, that's not what I'm saying at all. In fact, if anything, the better a player's regular season numbers, the better the chance that he's a clutch hitter.