My wife shoots all her family photos with a 50/1.8 on her DSLR. The tighter framing than normal really makes you fill the frame and think about composition. I'm the photo snob, she's the mom with the camera, and I think she does great (and her facebook friends and fam like her photos) It's also very smooth background and works well in low light without flash. Beats to pieces all the point and shoot cameras and kit zooms. All things that transfer to film use well. I mostly use a 50 as well, but I'm somewhat afflicted with GAS and are more apt to use lens variety and camera variety.

Anyone that was famous for liking their rolleiflex would indeed be a good example. Vivian Maier is a more recent example. Many famous photographers of old used rolleiflexes as a tool but not their only tool.

George Hurrell used a couple different lenses, but generally changing only after years of use. "Hurrell's Hollywood Portraits" describes him quitting a studio and taking his verito with him.