As others have mentioned, there are two main ways of scoring go today, which are almost equivalent. The questions you pose arise for Japanese/Korean scoring, aka territory scoring.
At the end of play, assuming that the outside White stones are alive, how many points does Black have in the corner under territory scoring?
Black has 4 points, 3 points of territory and 1 point for the dead stone.
Now, some beginners quite reasonably assume that you do not get points for dead stones, only for captured stones, and so there are only 3 points for Black in the corner, since Black has to fill 1 point of territory to capture the White stone. That would be a variant of go, but one that has never become popular.
Once you accept the principle that each dead stone counts 1 point, then there is no problem with counting the bent four stones without having to fill the opponent's ko threats first, just as it is not necessary to capture ordinary dead stones.
There is a problem if the opponent has a ko threat that cannot be filled first. Such unremovable ko threats exist, but are rare. Under Japanese rules, bent four is dead, anyway. The current Japanese rules have special rules of hypothetical play to determine life or death after play has ended.
Basically, a stone on the board at the end of play is by default assumed to be alive. The burden of proof that it is dead is on the player who would count it as a point. But proving death by capture does not mean that the player actually has to capture the dead stone at a cost of one or more points.
These potential problems with scoring have only rarely caused disputes between experienced players, which is why go went for centuries, if not millennia, without codified rules.
