Coaches might approache the semifinals differently.  You don't want an all out semi-final under the current set-up - you want some in the tank for the next day.  Athough it is interesting to note that historically the outcome would be the same, applying different criteria retroactively is meaningless.  It's like the people who complain every year that a team with a higher AA score didn't make finals as compared to one in another semi-final. If the rules weren't top 3, everyone would go into semi's with a different view of the competition.