I have been in the position of having taught students the difference between "less" for amounts (non-count nouns) and "fewer" for countable nouns and of being asked why the supermarket check-out sign says, "10 items or less." Hmmm... good point.... Good observation of the use of English in the "real" world! Maybe there's a sign-posting rule that says, "Whenever possible, use a one-syllable word" (even though the two-syllable word "fewer" is, in this case, more grammatically correct).
Unlike Stephen Fry, I still sometimes cringe when I hear someone on NPR (National Public Radio) say, "There's lots of people who ...." There IS lots of people...? Am I being pedantic if I tell my students that the correct expression is "There ARE lots of people who..."? We English teachers certainly have to choose our battles, don't we?
With all my students, I tend to say, "If you follow the grammar rule, you usually can't go wrong. However, language IS a living thing, and it's constantly changing as it is used by people around the world." That's about all I can say when I encounter text-messages, e-mail, Facebook comments, advertisements, signs and so on that break the rules I've struggled to teach. I do, nevertheless, appreciate the fact that my native language is quickly evolving as it spreads from neighborhood to neighborhood around the globe. Now, that's pretty exciting!