I think its important to point out that just because uses a backpack, it does not necessarily make him a "backpacker" in the context we are using here. Similar things could be said for those using skate/snow boards and not necessarily members of the skateboarder or snowboarder culture. I think "backpacker" is more a culture/style of travelling and it has little to do with the method by which one actually transports their belongings.
My experiences with backpackers indicates that they treat the places they are visiting like a zoo, rather than an amusement park. They choose to sit back (with fellow backpackers) and just look at the country and the culture, rather than actually participate in it.
I took one of the basic 3 day, $20 backpacker bus excursions in Asia with a friend of mine. The interesting thing is that my friend, who lives in the U.S. now, was originally from the country we were visiting. I was just expecting that the others on the trip would be interested in talking to him about the country and the culture. Afterall, they were there to learn, experience and ingest the country, were they not? But, much to my surprise, he didn't get a single question - or barely even a conversation - from any of them. They were just there to drink and watch the country pass them by.
Kind of left a sour taste in my mount WRT the backpacker culture.