Apostrophe S or not? Possessives and store names

Is it Nordstrom or Nordstrom’s? Kroger or Kroger’s? Sbarro or Sbarro’s? This fun article at MPR’s Marketplace quotes ANS Vice President Laurel Sutton about the confusion over possessives. What’s official, and what do people just assume? Here’s a sample:

Our minds tell some of us that it definitely needs the extra letter. That “s” — so brief, so unobtrusive, so natural sounding — sneaks easily into our lexicon. But oftentimes it’s unnecessary. (None of the aforementioned names are possessive.)  Adding to the confusion, sometimes companies don’t even follow their own naming conventions. It’s called “TGI Fridays,” but the company has also used the spelling “T.G.I. FRiDAY’s” in its logos and Nordstrom storefronts have displayed “Nordstrom’s” in the past.

Bonus: take the quiz at the end of the article to find out how many you know!