Because a potent allergy inducing product line could become a major health issue forcing Apple to take it off the market?
Not a chance. You know the metal button on blue jeans? Nickel alloy. That's how my allergy was diagnosed. I got a severe rash on my waist after a while from the little bit of metal on the inside of the pants because I never tucked my shirts in as a kid. I also have to be careful with belts, and I can't wear most watches.
Apple is just as likely as to be forced to take their nickel-containing products off the market as Levi or Casio. Ultimately it's buyer beware if you've got an allergy. You hope that companies won't put peanuts in their non-peanut cookies, or nickel in their metal devices, but it's entirely a business decision by those companies. At most they'll be forced to add a warning label to their boxes. We've got non-latex condoms for people with latex allergies, and platinum wedding rings for people with nickel allergies. I myself own a couple titanium watches. But companies aren't forced to cater to everybody with a medical problem. It's nice when they do consider accessibility, though.
I'm just hoping the iWatch isn't nickel alloy. I've been saying that for a while now, but I don't know if Apple is really aware of the issue. You can't exactly put a case around your watch. Maybe some attention over their iPads and people allergic to them will make them realize metal allergies are making it hard for a lot of people to use their products, and they can make better material choices.