Qualification of birth does not a good monarch make. Let's take a look at Nikolai II of Russia. He was born into a family that not only reigned but ruled, and was of royal lineage. However, the lack of preparation )among other things) caused him to fail rather miserably. I know that William will not rule, but that doesn't mean he doesn't need some sort of prep. I think he'll do a great job, because ha had the benefit of watching his grandmother on the job, and (I believe) is on the Privy Council, so there's the training in the state matters (he probably learned about the Constitution and the workings of government while at Eton/St. Andrew's [if the latter required all students, regardless of program to take classes in government/economics]). He also strikes me as someone who cares about others, and that quality is paramount for anyone who has a leadership role. When the time is right, he'll do his nation very, very proud.