I would bet that they have a lot more in common that you'd think. Just taking a look at shops across the USA and Europe, from mass market chains to department stores to boutiques, I noticed (and commented on) a trend towards homogeneity, as the interwebz allows information to disseminate more and more quickly. There are clearly still regional differences and differences delineated by economic status, but it seems to me much less pronounced than before. Language too, is becoming more and more homogeneous.
you don't think this says more about buyer/vendor behavior than consumer behavior?
I mean, you're likely to see more pronounced differences in the 35 to 50 demographic, as differentiation that began between 18 and 34 becomes more pronounced and engrained, but that's not to say 18 to 34 yo males are becoming more similar with time. if anything, I'd argue the reverse.