"Chemical-free" is an abbreviation of "dangerous chemical free," or in some cases (for car seats, not so much food), "chemically inert." Nobody would ever have a reason to specify that something should contain no chemicals at all, so the word "dangerous" is dropped in what is essentially an application of Huffman coding. ;)
Artificial toxin/poison/dye/fragrance-free. You can shove as much naturally occurring toxins in the product as you like, and both marketers and regular people will agree it's "chemical-free".
And that's side-stepping the whole "artificial" vs. "natural" nonsense. 'spacehome may be pedantic in this context, but in general, he's right - regular people have their model of the world ridiculously out of sync with reality. Which is of course readily exploited by advertisers selling "chemical free", "natural", "organic" products, which are no better (and sometimes worse) than the "artificial" ones, but still command a premium price.
