To be honest, most goth now days are well, just posers. They think goth is just wearing black and listening to bands like Marylin Manson and limpBiskit (sp). Whilst i don't mind people like that, i just hate the fact there only doing it just to be apart of the scene and couldn't care less for anything about what makes a goth a goth.
One thing you must understand is that being goth is about being unique, hence the black (cos most where colours). Goths do have colour, i mean i Have boots that have bright shiny red on them and spikes, and once my hair grows out a bit more longer i'm gonna get red streaks done. And whilst its not a requirement listening to goth/industrial bands like: BAUHAUS, Sisters of mercy, Siouxsie and the Banshees, Nosferatu, killing joke, etc it often a given as most other goths will probably ask you about them (plus there awesome bands any way so why not listen?). and for the record i listen to tons of heavy metal, metal, hard rock, alternative becuase i like it, as do many others.
To be honest a goth doesn't openly go around and say i'm a goth, we just tend to not saying anything unless some one asks. I usually give one of two answers depending on the situation. Usually i say i'm not a goth, i'm me but i associate as part of the goth subculture or i say simply yes i am.
One thing goths don't like is labels so a goth won't rally say there goth as it is a label, so thats a good way to see if either goth or poser.
I look at my self as being apart of the goth culture becuase my likes and dislikes fit in with it, not becuase i like things and dislike things a goth would. I'm not trying to fit in with the goth subculture, i fit in Because what i like makes me apart of the goth subculture..
In the end theres no real defining traits of what a goth is becuase there are so many kinds of goth, the best way to look at it is that every goth is apart of there own subculture and like to hang out with others of similar subculture.
Either way goths are unique from each other as thats what goths strive to be, unique and different from the conformists

anything else you want to know, just ask
P.S. Modern goths are as you put, are posers. Unless they associate with the goth culture out of choice and whilst apart of it do what they want, if there having to be told what to do to be a goth, then there just posers.