I watched this game (LOVE the WCWS, never miss it) and thought this was ridiculous as well. I thought the 'intent' of DBT was to kill the ball in areas where it is not easily/safely accessible by the defense (lodged in fence, into dugout, etc). That overthrow rebounded just fine, and, being right behind 1B, its going to see more than its share of overthrows.
I just don't get it.
BTW, Ive learned my lesson. I will never opine on softball rules again.