Difficulty selection will always be one of the cornerstones of modern gaming because it adapts the game to the user's skill level. Not all people who play video games are adept enough to play the intended difficulty, and some just plain don't WANT to. I'm one of those people; I prefer the easiest difficulty on the first playthrough so I can zip through the story and then go back and replay it for an actual challenge.
Difficulty levels are a double-sided coin: Not only do you get the easier choices, but you get the brutal ones like Heaven or Hell in Devil May Cry games. Just how some games might be a bit too hard for some people, they might be too easy for others. This warrants an additional difficulty to make the game more challenging, and what happens to the Normal difficulty? It gets known as "the easy one".