> If that is so, it's odd that everybody _writes_ <Peter's> with a
> detached clitic. Germans don't do that, afaIk (or do they? Anybody?).
According to the rule adopted 103 years ago (the official, i.e.
"amtliche Festlegung der Rechtschreibung" during Kaiser Wilhelm II's
reign): <Peters Laden, Peters Stube(n), Peters Bäckerei, Peters
Gaststätte, Peters KFZ-Werkstatt>.
However, most native-speakers will always prefer writing <Peter's
Laden> (giving... something on the Duden rule :=)). As one can see in
most localities all over Germany, Austria (and I expect this for South
Tirol, Liechtenstein, Schwitzer Düütsch areas as well as in
Lotharingia, Alsatia & Letzelburg, too).
Much the more today, when such "German" words like these are so much in
use: <sale! deal! dealer! price! discount! stylist! cash & carry! city!
downtown! handy! (this one is the German invention for "cell phone")>
and myriads more. :-)
(A similar pig-headedness here: most people tend to write <in's für's,
über's> &c., despite the fact that the rule has allowed & recommended
<ins, fürs, übers> for more than a century now.)