People usually want to feel a sense of belonging and most find a group to socialize and relate with. Small groups have a tendency to enforce conformity within them though; creating separate groups with their own enforced conformities; creating groups, cliques, and such.
When others notice the obvious differences of said groups and what they specifically compel others to conform to; It spawns a stereotype for that group.
The media usually only has the deal with the commercialization of these and the publicity of such.
This theory appears to be baseless. What is popular might be media driven, if not created, but when did the media coin a term that wasn't already in existence in at least some segment of the public?
They are all stereotypes created by the society we live in. Media creates some spin possibly....but I don't see the media forcing people to wear the cloths and perform the cultural traits associated with each counter cultural grop.