Honestly, I don't see the point of it either. I have not bothered to download 1.9. Some people want to level beyond 81, I guess. Don't see the point of that myself.
I guess one main idea is that now you can take all the perks in your "character relevant skills" (ie. those that fit the role you are playing) without having to make use of skills that are "out of character" --- like a warrior wanting to get more perks by leveling up their Illusion skill.
But I do agree that there's very little need for more than about 55-60 perks, and that's about 8-9 skills at 100. So there's really only a need for these Legendary skills if you play characters that are strong in the majority of skills, and you want to take almost all perks in all or most of those skills.