Nomercy, that's true. Generally these conversations are just for giggles. Most people that can afford to hunt big game, especially really big game, can afford to buy what they need.
I have known a few guys or talked to a few guys that have 'done it all' with one though.
Including a woman from Central PA. She took elk, sheep, moose, black bear, grizzlies, and lots of deer all with the same rifle.
Unfortunately I can't remember now what she used. It was either a .270 or a .30-06 though.
Last I spoke with her she was in her late 70s and still shooting a buck and a doe each season off the back of her chicken coop.
She also shot a pile of squirrel each year. 100+ every fall.
I could likely hunt my entire life with my .30-06 and never need anything else. It would certainly save me allot of money to do it that way. Unfortunately I have a curiosity about rifles and different cartridges. It keeps it interesting.
-Jake