its about time, American airlines will not have to face reality. I used to be in this business, and we always remember that at least 20 flights were scheduled to take-off at 13:30 (choose your major city airport). Now, you know that in the best of conditions there is simply no way that 20 flights will take off on time, some will, be definition, be 15-20 minutes late! This is in the best conditions, when the weather is perfect, and in reality add a bit of fog, rain or snow and all bets are off.
There is no reason today for flights to take off (on the hour) you can schedule your flight dispersion much better without affecting the bank systems that airlines use in hubs (don't ask). The joke was always that an airport such as La Guardia will have at least 75 days of bad weather per year (that's an average for the North East), doesn't include problem that will spill from other regions.
Airlines have in the past not worried so much about this, and have threaten that the new fines will force them to cancel flight -- GOOD, because cancelling flights is not a costless situation for airlines. Personally, I remember a flight between San Francisco and Las Vegas, the flight was 90 minutes late, speaking to passengers (and crew) I found out that the flight is absolutely never on time -- it is always 30-40 minutes late. It begs the question why didn't the airline shift the departure time by 30/40 minutes? Speaking to the then CEO of the airline, it was simply not a priority for them! They had more important things to think about (he was thankfully shortly thereafter fired -- turns out for using private jets...instead of his own airline to get to meetings -- he was a asshat!). The reality is that airline will now consider the separation of flight slots (its not the end of the world), in the case of some airlines they will create (not joking here) plans to deal with heavy delays (like having the home number of critical employees, and do some cross training so that in an emergency those missing can be replaced). Today's' $900k fine for American Airline sub is a first step to making flying in America more pleasant... you sure have a long way to go