I am afraid that the site does not explain it well.
It implies the if the word is plural it never needs an apostophe. This is incorrect. If if indicates possesion an apostrophe is needed whethe the word is singular or plural.
"My sister's cats" refers to the cats on one sister. "My sisters' cats" refers to the cats of two or more sisters.
When it comes to names assigned to things, I believe that the person who "invents" the name can do as he wishes. For example, Sainsbury's uses the apostrophe, presumably because Mr. Sainsbury wanted to indicate that it was his shop. An example where an apostrophe is not used where it could have been is the street name "Kings Ride". This could have been treated as singular possessive or plural possessive. But it is just a name and chosen without one, which is fine. The same applies to "Speakers Corner".
Thanks for the replies. I think fourm members' explanation seems to be the better one to me. But I did think an apostrophe was needed myself. However I will bow to the experts' replies and accept that it is not necessary. The heading will not annoy me as much now either. I hope! Really I should have known that the FE would have corrected it if it had been wrong.