Mexican versus Tex-Mex

Joe Drape of the New York Times has written an article on Tex-Mex cuisine in Texas. I must admit that I am a frequent violator of the category error that he discusses; my roots are from the border region of Texas (7 miles door-to-bridge, to be precise) where Tex-Mex and Mexican food are one in the same. Having spent a significant part of my teenage years wandering around the border region of Mexico (when it was still safe to do so), I am not sure that the line is as fine as depicted; at best, the differences are quite subtle.