Here's my answer you all would hate: it all depends... Hahahahahahahaha! Sorry, I Skujed it (you're big enough to take some sense of humor, right, buddy?). Seriously though; here's my take of Japanese style interpretation based on the Lydiard principles...
Marathon is basically run aerobically throughout. In other words, at that pace, you should be able to handle that stress relatively easily (except perhaps for pounding). Let's face it, if you can't handle that speed 3~4 weeks before the marathon for 30k or so, you should think twice about the target pace. Now, consider you are not completely freshened up, you're still somewhat tired so you cannot expect to run the exact speed you'd like to perform on the peak (hopefully) day. So if you'd like to run at 2:24 marathon, I'd say you SHOULD be able to run 30k at 2:35 pace COMFORTABLY.
Now, seriously, some people "gain" stamina from such workout; some people actually "use up" stamina from such workout. You have to figure out which type you are. If you are the former, it pays to do 30 or even 35k (32 is actually pretty good distance because it's "10k to go" for the marathon) at fairly solid pace. If this type run, say, half marathon, you tend to run fairly fast (because it's shorter) and you might go over the edge and by the race day you could be flat. In other words, just because ONE athlete had a success doing one way, that does not mean that's the best general way.
There are other type, in general, speed-type, who tend to use up stamina by running long. They could run far but at very easy pace; or even a half marathon is good but perhaps at "marathon" target pace. I don't know which type JB is but clearly he had pretty darn good success. Could he have run better with other program? Well, he just needs to experiment to find out. Again, in general, it's not the smartest way to tackle a new event on the most important competitions (Olympic Games?)--yes, some did pretty well (Zatopek?), but I would not recommend it. You want to figure out what works best for you.
How did I do, Skuj?