well, it depends on the definition of backpacker. like a young american travelling to europe backpacker or a serious i hike four days out into the wildnerness backpacker. between a sport backpackers bag and a standard campers bag - i'd say the difference is weight and loft. the "backpackers" bag being geared for performance, and the campers bag for fun, frivolus family-camping where space isn't an issue. now, a euro-traveller "backpackers" bag is just gonna be some shitty thin fleece sleep sheet, basically.
if you plan to camp or sleep randomly in a park or train station - get a real sporty backpackers bag, it will take you farthest all around, and they're damn good investments.
if you know you'll just be hostelling it, and it's summer time - just bring a sleep sheet, you can make one on your own, and it will be enough.
bend over to the front and touch your toes
bounce that ass up and down and get low...