Are you saying it hasn't? The cartridge has been around for over 100 years and for all practical purposes is a ballistic clone to traditional .45 colt loads which killed plenty of bears in it's day.
My skepticism doesn't come from being an internet keyboard jockey. I've killed a bunch of (black) bears in the last 25 years. They are NOT deer. Neither are they indestructible, but adult bears are not going down easily with an inferior caliber -- of which the 45acp most definitely is (when it comes to bears -- otherwise it's my go-to carry caliber).
I think it's irresponsible to say that 45acp can do the job easily on bears, and I don't mind saying so. Sure, bears have been killed by 22lr. But I'm not going to count on one when hiking / hunting in bear country.
That said, whoever said that even NEEDING a gun for defense agains black bears is almost ridiculous is right. They're a very common animal, and attacks are rare. I've encoutered sows with very young cubs, and they did nothing but retreat, or bark for the cubs to climb a tree and shuffled off a distance, waiting for me to go away. They aren't grizzlies, and they generally are not aggressive (the last one I shot in Maine is another story for another day..). The problem is that when black bears DO attack (and yes, they kill people), the attack is often brutal and tragic. Black bears rarely bluff charge like a grizzly, and they rarely attack just because you're near their cubs. BUT they do attack to eat you. Google the attack that occurred in a Canadian park -- old bear, bad teeth, human fatality.
It happens, and it's wise to be prepared for it. Will a 45acp kill or incapacitate a black bear at point blank range. Probably. But are you willing to bet your life on it?