The reason for this language peeve is that grocery store items are items that can be counted. Any number of grammar sites and blogs will tell you that the word less is used with mass nouns and the word fewer is used with count nouns.
For more about the difference between mass nouns and count nouns click here.
The reason I bring up this prescribed rule is because of the exceptions to the rule.
My son recently asked me why, if numbers can be counted, are the phrases greater than and less than used in mathematics.
Well, every rule has exceptions and according to Washington State University "the exceptions to the less/fewer pattern are references to units of time and money, which are usually treated as amounts: less than an hour, less than five dollars. Only when you are referring to specific coins or bills would you use fewer: 'I have fewer than five state quarters to go to make my collection complete.'"
Based on this analysis, if I said 8 > 3, I would be comparing the amounts (or mass) of the two individual numbers and not talking about the counting of (1,2,3,4,5,6,7,8) of the numbers.