Thank you, I'll remember that next time I pay a visit to Sainbury's's!
My point isn't that all business names are treated that way, just that the ones that are the reason is grammatical tradition not (for the most part) people who incorrectly think the shop is called "Tesco's" or whatever.
There's been an historical transition from small chains owned by individuals (e.g. the Victorian Mr John Sainsbury) to big brands (e.g. Superdrug), hasn't there.
The possessive apostrophe was appropriate for the former but surely less so nowadays. I would guess "Sainsbury's" was a rebrand intended to reflect tradition.