My point about it working (after reading the entire wiki entry) was that it did indeed work when they got around to actually use it, rather than try to beat the bear off with a stick.
Another thing to the story is that the guy failed to have his arm up so the bear couldn't go at his throught, and it was supposed to be a "wrestle match", so the bear had more than enough opportunity to get very, very close without anyone even attempting to do anything. When they then failed to follow safety procedures (aka spray the freaking bear) and instead tried to beat the bear with a small stick (******!?). What is good about that video is that if they had sprayed almost instantly, the attacked would have had much of a chance of survival.
There is very little chance of meeting a bear in nature that not only get's that close, but also have you not have your arm up in defense. If you had a spray or someone near you had a spray, you would have it drawn before the bear comes that close, or you would at least have your hands up in a defensive position.
A gun would probably not have helped either, assuming you actually hit with a kill shot, if you take into account their behaviour. I mean, if the man had still failed to have his arm up in the proper position, and they had still first tried to whip the bear into submission as it happened.
It did work to stop the bear, even if it had been enraged by being whipped. If only they had sprayed the bear the instant it attacked, as I'm sure they had planned to do.
No, bear spray is not a guarantee, nor is a gun. But after seeing that video, it is very evident that it works, and works very well. Of course you have to actually spray it for it to have effect. But the same applies to a gun.