Age-ranging on the back of children's books

There's been much discussion about age-ranging on the backs of children's book, both here and in the UK, where the suggestion has originated.

Here's a link and here.
and the lovely Emma of Snowbooks has this to say.

I heard that one bookseller was circulating a petition against it at the ABA conference on the weekend. We (black dog) aren't thrilled about it - short-term gain for long-term loss is our feeling. It may (and there doesn't seem to be that much proof of even this) sell more books now; but at the cost of selling more books later. Also I can't see that research done in the UK has relevance to our quite different market here. Maybe colonialism isn't as dead as it should be.

But Variety had a view on film ratings that's interesting in this context:
"a new twist on the PG-13 rating -- one that strongly cautions not only those under 13 but anyone much above it, too.