Regarding this website...

To be clear, from what I've heard about stats in the United States, "what allergy" is uncommon (not sure the number), "Coeliac disease" is more common (estimates are something like 1 to 3 people per 100), and "wheat intolerance" is pretty common (estimates are something like 1/4 to 1/3 of the population).

I do not have a source for these numbers, I am writing them from memory, so they may not be correct.

Also, while some people use the defiintions given on this site (which are correct I believe), some people lump wheat intolerence with Coeliac disease (and some even confuse it with wheat allergy). Others assert that such classifications don't even make a lot of sense because it is actually just a spectrum from mild wheat intolerence to all-out Coeliac disease (but that wheat allergy is a different beast). I don't know enough about the issue to make a value judgement about the classification system.

I do know for sure that I feel better when I eat less wheat and feel worse when I eat more. This personal approach not a scientific approach, because the sample size is low (I am only one individual, and I only compared my wheat intake to symptoms for a few months before keeping it low since), and there are so many other variables that I don't really account for, and it's not blind so placebo can play a role.