I have never read Mr Eberhart's book but assume he is talking Primary scrapes, not to be confused with secondary or boundry scrapes. Now as MeanV said in his post, in some places scrapes are scarce to non existant and I also belive this to be because of poor buck to doe ratios. Sometimes a short drive to another hunting area can show a big difference in scrape activity.
Primary Scrapes are like any key pice of property with humans, animals or even fish, if one is removed, another will move into it's spot unless there is some sort of pressure put on them not to. A good one usually has great rub lines going to and coming from it, and you can see where the trees are scarred from seasons past, if your lucky from the same buck from seasons past. Most, Even if they are not being cleaned out or pissed in get checked during the year and you can tell by the fresh tracks and broken twigs on the branch above the scrape.
I killed a good buck back in the early 80's that was cleaning out a primary scrape for the first time that season, most hunters would have never looked at the spot twice.