[Travis]

For comparison's sake (in defining an umpire's involvement in a play), consider this something like missing a base (including home) when running the bases. If a player is on second when a hit occurs and scores on the play (but doesn't physically touch third base on the way), the run counts unless the defensive team appeals the play. The ump "knows" (or should) that the runner didn't touch third, but can only make the call once the appeal has been made.

Whether the system/rules should be that way, again, a different discussion, but the way the rules are written now, that's how it's enforced during play.