We won't see another IE6-like situation again. It was created by a lack of foresight, similar to the Y2k bug. Nobody is going to upgrade from IE6 to IE7, they will go to the most current browser and the circumstances that led to the current problem are most likely removed.
Chrome has an excellent model for installation and updates, if the other browsers follow suit, all for the better. Easier said than done, but if the user won't update their browser to one of the many free choices they have, F 'em.