Though castling does take all kinds of strikes in passing into account for the king.

True. It's as if any piece could kill the king in transition.

And yet other pieces can't kill that pawn in passing. Only another pawn.

We shouldn't try to find too much logic.

Clearly there's some Heisenberg uncertainty principle where the pawn occupies both the third (or sixth) and fourth (or fifth) rank, in a kind of superposition that only an opponent pawn situated in a certain position would be able to observe.

I think the logic is based on pragmatism. A different piece has a chance of capturing the pawn later, but a pawn would never be able to since it can't go backwards.