Michigan's history of possessive company names all began in the early 1900's with the Ford Motor Company. The Ford Motor Company was owned by Henry Ford and therefore the factory was known all over Michigan as Ford's Factory. If a person was asked where he or she worked the response would be, "I work at Ford's." Too keep things simple, in written communication the apostrophe was dropped, thus Ford Motor Company became Fords.
One thing always leads to another, hence Meijer became Meijers, Kroger became Krogers, and oddly, K-Mart became K-Marts (though we all know there is no K-Mart family, it is the Kresge family, so technically it should be K's-Mart).