As a three-time ironman finisher (Wisconsin '04, Lake Placid '06/'08) this is spot on. The key is long, slow, boring training, keeping your eyes glued to your HRM to stay <zone 4. It's also why a lot of first time ironman racers don't do as well as they trained for since they tend to get caught up in the moment and go too hard, go anaerobic, and spend the rest of the race paying for it.