A couple of points...
The Magic Mile is designed to be run at 80-85% of your maximum effort, not as fast as you can. When you finish the mile, you should still be capable of running more, but not much. It is a useful tool for determining your PREDICTED finish times for both the half and full marathon, when run under proper conditions (no injuries, etc.)
Once you've determined your pace, then you figure your training pace (per Galloway, 2 minutes per mile slower) and adjust the intervals accordingly. But, as many have said, it's all up to the individual. Generally, shorter intervals correspond to slower times, but Jeff is running much faster times with :30/:30 intervals. People who have run with him say he is FAST during the run segment.
I run with a Galloway program locally and am a group leader for one of the pace groups. We obviously have to adhere strictly to the posted intervals for each group during our training runs, but once we get to our races, we all do our own thing. I tend to use shorter intervals during races, similar to what Jeff is doing now. And as skeptical as I was about the MM, last year I took an average of the 4 that we ran during the season, plugged it into Jeff's spreadsheet to find my predicted race times, and it was absolutely dead on for the 5K, half, and full. Scary.
Jackie