It is common on that calibre. It was also available as a separate item to put on other calibres. It is often called the "smokeless sight" in error, simply because it has the word "smokeless" on it. The .32WS was designed so that you could shoot factory smokeless rounds through it, then reload them with black powder and lead bullets.
Of course, there was no way that you could hit the 100yd. target with BP loads from a smokeless sighted rifle (think the sights on the .30WCF.) The .32WS sight allowed enough adjustment that you COULD shoot BOTH smokeless and BP loads without installing a new set of sights. The "Smokeless" and "50 and 100yds." was the setting for factory smokeless rounds. For BP, you put it almost all the way up. For some reason, people seem to think it was a special sight for smokeless powder, when, in fact, it was a special dual purpose sight.
Book value be danged, there is nothing whatsoever wrong with the .32WS, and it is a very interesting calibre. Collectors are a weird lot, they disdain round barrel rifles too, even though there were 9 octagon barrels made for every round one. And the .32WS was the least common chambering. Go figure!