Except when the government makes it illegal to tell customers about it.
When I read this, I'm less convinced that New Zealand is outside of the asylum. Here's Scott Anderson on labelling problems at Kereru Brewing.And to think, just a couple days ago, I was making fun of America for its beer label dictator.
These regs don't come in until 2016 so there should still be time to fix this. It sounds like gluten is in the unhappy spot of being something not quite serious-enough to be an allergen but probably more important than a "health claim". Were it an allergen, then everybody would be required to put on labels saying "May contain gluten". If it's not an allergen, then nobody's allowed to advertise "gluten-free", because it's bad to associate healthiness with beer, even if moderate drinking is healthy.
If that doesn't work, perhaps SOBA could produce a list of Gluten Free beers, and whatever organisation exists for the no-gluten people could link to it.