Nordstrom, his store

Many company names explicitly identify themselves as belonging to (in a grammatical sense) someone. Taking a walk down the street here, I can see:

McDonald's
Macy's
Papa John's
Trader Joe's
Wendy's
Schuck's
Chuck E. Cheese's
Fantastic Sam's

... and others too numerous to mention. The antecedent, as it were, of the possessive is sometimes explicit (Papa John's Pizza, Schuck's Auto Parts), but is often implicit: McDonald's ?restaurant, Macy's ?department store, Trader Joe's ?emporium, Fantastic Sam's ?tonsorium, Chuck E. Cheese's ?den of prepubescent dining.

The pattern of possessive name + (implicit) emporium is so strong that people follow it even when the name does not formally include the possessive. In my youth, we often shopped at Montgomery Ward's (or just Ward's), as everyone called it, even though the official name is just plain old Montgomery Ward. Likewise, you might have a hard time convincing some people that it does not say "Nordstrom's" on the side of the building. Although not everyone believes me, true old timers in Seattle -- aka Jet City -- will still refer to the aircraft company as Boeing's. If you listen with this in mind, you'll undoubtedly hear people whacking an extra -s onto the end of local establishments in your area. (Seattle: Pagliacci['s] Pizza, and the occasional and jaw-clench-inducing Pike's Market.)

To get a phantom possessive, it appears that the name must be clearly identified as the name of a person. In Seattle, people used to shop at Frederick and Nelson's. But people don't work at Microsoft's, or shop at Wal-Mart's or Target's, or buy their clothes at Old Navy's.

If the name includes an -s, then there is widespread confusion. Just for yucks, I googled for "Sear's +store" and got around 29,000 hits. Some of these refer to stores whose actual name is Sear's (e.g. Sear's Shoe Store), but from browsing the first few pages of results, it looks like most of the mentions refer to the erstwhile Sears Roebuck. You will also find the name Marshall Fields (now Macy's) written as Marshall Field's.

All of this, really, just to ask this question: why isn't there an apostrophe in Starbucks?