Gluten?!

Can someone explain to me what gluten is? I thought I had the basic idea: proteins in certain grains and flour responsible for elasticity and chewiness. Some people are allergic. I understand the nature of gluten, how it is produced, why dough needs to relax after kneading, and that some people are allergic to it. What I DON'T understand is why EVERYTHING nowadays that does not have gluten is labeled gluten-free. For example, at the school cafeteria the other day the green beans were advertised as "gluten-free" and so was Tito's Vodka in last month's Saveur. Is this valuable information, in which case I'm missing something about the nature of gluten, or is it just American marketing gone amok? I understand that some people are allergic and want to avoid certain foods that may (or may not be) glutinous, but was there any real doubt about the green beans or vodka? I feel like I must be missing something here.