Penney's was founded by James Cash Penney. The store was his store, that is, it was Penney's store. I think the omission of the apostrophe was kind of artistic

Penney's was founded by James Cash Penney. The store was his store, that is, it was Penney's store. I think the omission of the apostrophe was kind of artistic license, but I'm only addressing the silliness of adding the "S," with or without an apostrophe, to something that isn't a person's name.