And from what I can understand, Canova says that once you're more than 10% away from race pace, you're no longer doing specific training for your event. If I'm understanding Canova correctly, that would mean that for a 2:12 marathoner (~5 minute pace) 6:00 and 8:00 per mile don't really have a different aerobic effect. So if you're doing a recovery run, since you're going slower than 10% of marathon pace, it doesn't matter how slow it is as long as you recover.
And, as I and now someone else has mentioned, Nate is probably a little overly cautious with estimating the pace of his runs.
I'm not saying he trains perfectly, because no one does, but this is a guy who wasn't even a DII All-American in college and now he's down to 2:15. Yes, he's having a lot of trouble right now- but to claim Nate isn't serious about the sport is ludicrous. Also, what he's doing NOW shouldn't be taken as what he does when he's totally healthy- right now he's got several injury issues, his health isn't great, his fitness isn't where he wants it to be, and in 6 or 7 weeks he's representing the US for the first time in international competition in an insanely competitive marathon.
Read some of the comments Nate has left on the blogs in answer to questions people have- he clearly knows what he's doing, it's just that real life will, on occasion, interfere with what we would like to ideally do in training. Well, real life- getting sick, getting hurt, having a crappy night sleep, doing a run with your girlfriend, etc- gets in the way for some of us. Clearly, Nate's many 2:08-marathon detractors on this thread are always perfectly within the parameters of the paces formulae predict for them and never have rough patches.