I was at trials in 2007 because I had a friend running and I ran New York City Marathon the following day.
I had never seen anything quite like what Hall did between 15-26.2. He was running the hilly twisting course in Central Park in 4:30's-4:40's. When he saw Kannouchi in the jumbotron behind his pack of 4 as he passed 15 miles he opened it up. The last mile or two he had his hands up in the air most of the way with absolutely no concern about his pace and was still running fast. The last half despite waiting to take off at 15 was 1:02 low. He literally jogged the first 7 miles letting guys like Wardian go ahead of him. On paper it looks different of course.
Catching him in the last 5k? Not a chance that day. Rupp would have had to take it out from the gun to have beaten him. So I don't know but like KingAdRock said you had to be there. To me it looked like of he had wanted to in the last 5 miles he could have dropped it to 4:20's without a problem.
After watching him I was convinced he could have run whatever he wanted to run that day. A lot of you guys are just looking at his 2:09 thinking that Rupp could beat that. So could have Hall by a lot if he went early or pushed late even on that cr@ppy course .