I think a culture is predominantly the result of a groups history, and we have quite a history. Much of what I would consider to be 'gay culture' is slang, references and recurring events, like pride. There are a lot of cliques in every group which the general public ascribes the same group culture and I think that's the same for the gays. The 'group culture' is largely the same for the different cliques, the problem is that some cliques are louder than others, making the general public adopt their aspects as being part of the group culture. That's pretty much what caused the predominant stereotypes.
Our history is what is the same for all gays and I think that is what makes our group culture. Everyone, including we ourselves, should be careful to ascribe subculture traits to the entire group.