@grayson
Right, I'm not saying that they don't. I created one too.
What I'm saying is that the specific example has a flaw, I think, in that the example says that the king's children won't inherit a title from him, his sister's children will.
But if the king has a sister, why would he be king at all, since she would be the one entitled to inherit in a matrilineal society? Wouldn't he only be king if he didn't have any female siblings to inherit ahead of him? And in that case, what happens when the king dies? When a queen regnant died, her firstborn and/or male issue would inherit regardless of parentage, even though queen regnants were not the preferable situation through most of history.
So.
Anyway, hopefully that makes it more clear. If there is a King Regnant, then presumably there are no female siblings, so 'his sister's children inherit everything' makes no sense.