I don't think they claim you'll be less tired, but there may be a reduced chance of injury, and the fatigue will be of a lower level. I know from personal experience that after a 20 miler I'm basically a couch potato the rest of the day, whereas after 15 or 16 I'm just "pleasantly tired."
And no, it's not necessarily the best or only way to train for a marathon - just a viable alternative, and one that's fairly different than most traditional plans.
I know there are many people who find something that works and stick with it religiously, and that's fine. I'm one of those other types who's always looking for a new and possibly better way to skin a cat. And if it doesn't work, that's fine too - for me, the process is as much, maybe more, fun than the end result.
As George Sheehan said, we're all an "experiment of one." What's wrong with breaking away from traditional methods to try something different? Given that the body tends to get better and more efficient at doing the same thing over and over, a fairly radical change might be the impetus that is needed to jump start some improvement.
Sorry if the tone of the article was misleading, but in order to get people's attention, you have to grab them with a headline like "the myth of the 20 miler" or Kevin's statement that "20 milers are a farce."
Given the length of this thread, it's obvious they've succeeded in at least getting that attention.