On carb counting vs. glycemic index... one is a heck of a lot simpler than the other. Someone starting out on Atkins or a similar plan is probably already overwhelmed with all of the information, and will probably have a much easier time simply counting carbs. Glycemic index and load, though, are more complex. They involve food combining, cooked vs. raw, etc. That's probably why it isn't discussed in DANDR but is in Atkins for Life.

By the time you don't need to count carbs anymore, you probably don't need glycemic load, either. You know by how you feel whether or not a certain food is going to cause you problems.

MHO.