Possessives for words ending in "s"

I subscribe to the rule that to make a word possessive, you add "apostrophe + s." Even when the word already ends in "s," this is the rule I follow. With a few exceptions (Jesus, Moses, Achilles, etc.), this rule is widely supported in English style guides. See, for example, Garner's Modern American Usage at page 624. So I write--

Schiess's house
my boss's car
Jones's document

Only when the word is plural and possessive do you place the apostrophe outside the "s."

the Schiesses' house
the bosses' cars
the Joneses' documents

But many students and many lawyers I teach do not follow this rule. Their practice is that any time a words ends in "s," you put an apostrophe after the "s" to make it possessive.

Schiess' class
my boss' car
Jones' document

I don't like this, and I have wondered why people do it when it isn't right.

I just figured it out.

Newspapers use and thereby promote this form. (It may be because of the AP Style Manual's recommendation.) So we read the newspaper and learn this incorrect form. Eventually, incorrect usage will predominate and we'll abandon the traditional rule. Or have we already? We already see the practice spreading from words ending in "s" (like Hays below), to words that end in an "s" sound:

Hays' leader
Gonzalez' opinion
the Red Sox' manager

Yuck.