Liz - there are two different reactions to gluten and even casein in some cases... one is celiac (gluten) and one is the gluten-sensitivity issue.
Paleo eating has been around for a very long time...it's not a fad. If your body makes antibodies to food protein molecules, it's very damaging and manifests in a myriad of health conditions, may of which are not recognized as coming from that source.
I have a report on this topic sitting half done on my computer. Eventually, I'll post it in an attempt to clarify the misunderstanding about the difference between celiac and gluten sensitivity.
Jackie