As a celiac, I wish it were more common.

Celiac in the US shockingly misunderstood. The current gluten-free fad doesn't help.

Of the places I've visited since being diagnosed, Italy was BY FAR the best for eating out while celiac. Rome has some of the best gluten-free pizza. Florence was no slouch. And if a restaurant is not comfortable serving you (small kitchen, impossible to clean properly, not trained, whatever), they'll tell you up front so you can go elsewhere.

I think its legally required in many places. In others it is about not being sued. And for all kitchen staff it is fairly important not to poison people!