A commenter on the reference to President's daughters thread writes:
The grammar seems more troublesome than the mention, without name or likeness, of the President's daughters.
I am open to education or correction, but would not "healthful" (instead of "healthy") lunches for students be the proper usage as well as a worthy goal?
Fortunately, a standard reference source gives the answer. If you go to dictionary.com, you'll see that both the Random House and the American Heritage give "conducive to good health; healthful" as one meaning of "healthy." And as a special bonus, the American Heritage entry is followed by this Usage Note:
The distinction in meaning between healthy ("possessing good health") and healthful ("conducive to good health") was ascribed to the two terms only as late as the 1880s. This distinction, though tenaciously supported by some critics, is belied by citational evidence — healthy has been used to mean "healthful" since the 16th century. Use of healthy in this sense is to be found in the works of many distinguished writers, with this example from John Locke being typical: "Gardening ... and working in wood, are fit and healthy recreations for a man of study or business." Therefore, both healthy and healthful are correct in these contexts: a healthy climate, a healthful climate; a healthful diet, a healthy diet.
Of course, if one follows the Horace Google principle, one can see why it is the poster writers said "healthy" instead of "healthful": "Healthy lunch" yields over 100 times more Google hits than "healthful lunch" does. Sticking with the most common usage is generally better for advertising, I think, because the less common usage seems likelier to distract the reader from the substance. (There are of course exceptions, for instance if the advertisers want to stand out through their unusual word choice, or if the more common usage is intensely objected to by a substantial minority of readers and the less common usage is not intensely objected to by a majority. But I take it that here they were just following the norm, deliberately or otherwise; and the commenter's objection is a pretty rare one, as the extremely lopsided usage data shows.)
But in any event, the moral of the story: Before you make a claim of usage error, or even usage "troublesome[ness]" (by the way, the issue here is not "grammar," but usage, since both "healthy" and "healthful" are adjectives), look it up.