Vampire rulers no. Very old and powerful vampires that get to make the rules yup. So you would be splitting hairs. In Twilight the Volturi are old and thus powerful. The book doesn't expand on why the correlation exist, but it does mention that they are royalty. In Vampire Diaries the older the vampire is the more powerful it becomes. I respect your opinion, but I must disagree. The Volutri are always looming in Twilight, but take up very little of the four books. The are used to drive the plot. If it weren't for them the plot for the last book would be lost. Having said that they don't appear until the final 50-80 pages or so. They move the plot along without ever having to appear. So yes to some degree they are important, but there just not around often enough in the books for me to agree with the statement that they are the main theme. It's like the shadow monster in that stupid TV show Lost. It's there and people make choices based on it's presence, but you almost never see it, and it really doesn't do much.