Here is an interesting article that pertains to this debate:

http://www.bellinghamherald.com/2012/07/31/2625200/is-your-problem-gluten-or-faddish.html

It seems like it is two-fold: part of the surge is that cases of celiac disease are increasing, and part of it is fad.

As for Domino's, I say they're going to do what they find profitable. If there's enough customer demand, they're going to respond to that demand. It doesn't affect me whether or not they host the option, since I don't require nor seek gluten-free foods, so I don't really have a strong opinion on this one.