The other consideration now is that with groups of three teams, you will have a situation (regularly enough, I reckon) whereby two teams play the final game knowing a draw will send them both through, leaving the third team stranded purely because the luck of the draw dictates that they miss out on the final game.
Possible scenario -
Game 1: A v B - Score 0-0.
Game 2: A v C - Score 0-0.
Game 2: B and C each know that a loss will knock them out but a score draw will see them both qualify.
After Spain '82, I thought this was the whole idea of playing final games simultaneously?