Disagree. Many elite athletes are not super scientific about their food choices [1]. Instead they eat what they crave. The human body is pretty good at figuring out what it needs nutritionally.
That being said, there is a lot that is important off of the field (e.g. sleep, stretching, etc). Just nutrition is fairly low on that list.
As much respect as I have for triathletes, they aren't really representative. Food choices are incredibly important for athletes in weight class-limited sports (eg wrestling) or where muscular hypertrophy is important (eg powerlifting). Gymnastics is another one. Believe me when I tell you that coaches have diet absolutely dialed in for many classes of athlete.
That being said, there is a lot that is important off of the field (e.g. sleep, stretching, etc). Just nutrition is fairly low on that list.
[1] http://www.active.com/triathlon/ironman/Articles/Nutrition-T...