This is the reason for the British explanation - some grocers' stalls have this error on every placard.
They seem to be the worst.
They all advertise Apple's, Pear's, Lemon's, Orange's etc etc etc!
.(I've just noticed the grocers' apostrophe in the word "snowmobiles"!) English grammar is dead.........
A phenomenon in German language, too. Interesting to see that you call it "grocers' apostrophe", we call it Deppenapostroph (twit's apostrophe).
Can't imagine where you found that..
That must be the worst English I've seen in a long time!