To me, training is like putting all the pieces together and the race is your presentation. You put acting, then music, backset, lights, then costume and all... Finally on the opening night, you put them all together. You have endurance, speed, pacing, tactics... You work on each element and in the end put them all together. In other words, you really don't want to run as far and fast on your training. Now, you might go further than the race distance (even for marathon); you would certainly go faster than the race pace here and there. But you just don't want to run as far and as fast on your training run. Your race should be a peak form. If you do that on your workout, where would you go from there?
Marathon used to be a serious athlete's race. They train very hard and they peak for the race. They don't run their long run of, say, 22 miles at the marathon pace. It is their stamina training so they would go sightly slower pace. You might even go close to the race pace like tempo run of, say, 15 miles. But it's still not "THE" race. They'll have some reserve. Meanwhile, they'd hone their speed by racing, say, 10000m at cosiderably faster pace than the marathon pace. That could be their speed work. Shorter ran 27:45 for 10. I can't remember his 5k PR but I'm sure it was somewhere around 13:30 or even faster. One year at Fukuoka marathon, he blasted out in the first 5k in 14:35! That was unheard of; but it was still a minute slower for him (he slowed down but still won it in 2:11). They could easily run the marathon at 5-minute pace and, most likely, they would train their long run at 6:00~6:30 pace.
Now, marathoning has changed so much over the years. Not only majority of people have any idea of "peaking", they probably don't even have a concept of "sharpening". To most of them, "sharpening" for marathon means doing something like 6X800m at sub-10 minute pace (5 minutes). That, to me, is the currect situation. But for some reason, whoever is adovocating it, this "do the long run at 1:00 slower than your marathon pace" stayed. I'm sorry, but, to me, for those who expect to run the marathon in 4:00~5:00 is more of an ultra category. Particularly if you do run/walk (and I would like to clarify; I'm not against run/walk, and I understand they ALL train very hard as well), their marathon pace IS their endurance running pace. I really don't see any reason for adding a minutes over their marathon pace because they wouldn't be peaking or honing their "sharpness".
Now, there is another way to look at it. I've noticed, even for 4-hour runners, if they peak right, their pace naturally comes down. It's not uncommon to see a minute per mile drop just by tapering. In fact, if this does not happen, it's either you're training too fast; or you're too tired to get that extra out of you naturally by tapering. Again, it should come naturally. You cannont plan for it by thinking, "Okay, I should be running a minute per mile faster if I taper well so my marathon time should be expected to be such-and-such based on my training run pace...." It doesn't work out that way. It's the other way around. I honestly think most people who jump to run a marathon train way too hard. As far as I'm concerned, if you're training at, say, 9 minute pace for most of your runs including recovery jog and long runs and running the marathon at 9:15 pace, there's something wrong with your whole program.
