In my experience, it can go either way. I believe this is one of those rules that is actually in transition due to common usage today.
I think BR just nailed the whole argument down with this statement. It is in transition due to common usage.
First, the "rule" was, if it ends in "s" place the apostrophe AFTER the "s" to indicate possessive. THEN it was, if it ends in a vowel
and an "s" add the apostrophe after the "s" but, if it ends in a consonant and an "s" add an apostrophe AND "s" at the end. Lately, we have seen the further metamorphosis of the apostrophe "s" conundrum in that many now use the apostrophe "s" following ALL "s" ending words.
Much of this (and I apologize if I offend anyone) is due to poor education starting with the teachers who now "educate" the schoolchildren. Certain grammatical standards are flexing and adjusting based on the common denominator. The teachers of today's children learned a slightly different standard of grammar and language from their teachers who, likewise, learned things a bit differently from
their predecessors. So it is not unusual that what you learned in school about the proper way usage of the poor s and it's friend the apostrophe might be different from what someone else learned.
Now, having gotten everone's hackles up, let me say that I believe language is a living thing. It changes as the society that uses it changes. It adjusts according to the demands of the sulture in which it is used.
Consider that Olde English was based in German and in no way resembled even Middle English, much less the Modern English we know today. In fact, what is called English is America is referred to as American in Great Britain because it is not the same language as that used in Great Britain (England). In America, a bonnet is what ladies used to wear on their heads a century or so ago. But, in England, it is where you find the motor of your car. A boot is what an American would put on their foot to keep tootsies out of rain, mud, or snow. In England, it's where you keep the spare tire for your car.
English, like any other living thing, is constantly changing. So, if you see that 's as being used one way while someone else argues for a different construct, it's okay. It's just the ever-changing world in action. Go with it.