Sausages are a staple of German street food, and yet most places serve sausages in a round "semmel" bun. But the sausages are long (duh) so they just beg for a longer bun. Why do you think hot-dog-style buns aren't more popular?
Just my observation bit most Germans eat with knife and fork.
Also, wouldn't work with Currywurst (think of a cut up sausage in enough curry sauce to drown a good size...we'll...it's too much sauce.
Cheeseburgers...I've only seen them eat with knife and fork.
But that's just my observations (limited as they are)