I bought the book today. Looks good.
It's not uncommon for top runners to do the majority of their running (I didn't say "most" because i think they do more than 20% quality, but probably not more than 30%) at a relatively slow pace. Of course, "slow pace" for some of them will be unbearable pace for some of us regular people.
Sally Kipyego of Kenya, who finished second to Tirunesh Dibaba in the 2012 Olympic 10K, is said to run a LOT of her miles at well over 7:00 per mile. (I remember reading this, but I can't remember the article.)
I think the book might be especially valuable for those of us in our 40s, 50s (like me), and beyond. When I was younger, I used to feel that all my runs, even the recovery runs weren't much good if they were less than 6:00-6:30 per mile. After reading a lot from experts, I've come to the belief that a lot of our miles should be run relatively slow, at a conversational pace, while our quality running should be real quality. And I believe that if we run our easy days slowly, we can really kill those quality sessions. For older runners, especially, it makes sense for our easy days to be genuinely easy. An example I like to use is a weight lifter. Would a weight lifter hit chest and biceps really hard today and then feel like he had to still put in a good workout on chest and biceps tomorrow, even at lower intensity? Of course not. I think the same thing applies to running. Easy is easy, and hard is HARD.