I find it funny how it all boils down to symbolism. What we symbolize for others though what we wear. If you want to show others that you go for nonconformism then you have to use some common shared language to get that across - and that then just ends up being reused a lot. A hipster will be more comfortable around others dressed like themselves because they then feel they have something in common: nonconformism, among other things. It is not the clothing themselves that makes them stand out from the mainstream, it is how they feel on the inside. The (identically looking) clothing just represents that inner world.