Never mind - he's done a 28 miler before - in 2007 training for the Trials. Yikes. I can see why he's pretty much given up on the marathon.
11/2007:
"RW: Did you go back and look hard at New York last year to figure out what you did or didn't do right?
DR: I was looking back through everything we did and I look back through my log this year and it's amazing the amount of difference of mile spent at race pace and total runs that have been equal or almost equal to the distance of the marathon. Before, a 20-mile run at altitude was a long run and it was hard. Now, I've done up to 28-mile run in this training block, which is something I would not have been able to do and now I've run 24 miles at almost the same pace that I ran for the marathon last year."
http://www.runnersworld.com/cda/microsite/article/0,8029,s6-239-569--12270-0,00.html