Where is the guarantee that royalty behaves any better than anyone else? What about Princess Stephanie or Ernst of Hanover? Manners and breeding can come from any class (or not!)- they come from inside a person, not from their ancestors. I don't see anything "common" in Kate Middleton- she's smart, educated. pretty, and seem to have a good relationship with William. And they started out as friends, which is a great "plus" for any marriage. I have no idea if they will marry or not, but if they do, I'm sure they have the basis for a successful partnership.
True:). But in my opinion, they have been trained since birth for the position they are to ultimately occupy whether that be Queen, Princess or whatever 
. Also it would give a more firm foundation to any relationship with the princes. They would better understand what its like to be in the spotlight. Please we don't what another re-run of the Diana years. They are important members of the Royal Family and I think they should really be marrying the creme de la creme!! Of course happiness would be a big factor too.. 
But have they, any more in this day and age been trained for such a role really (apart from the ones who are heirs to the throne, of course)? Younger siblings and cousins of monarchs in this day and age are more or less encouraged to have private careers of their own- very few live off the public purse entirely (and would be considered free loaders by many if they did). And those from exiled royalty certainly have had no more experience in ruling than any one else.
I come from a long line of peasants/farmers, miners and a few fishermen going back a thousand years. Do I have any innate knowledge of plowing a furrow, digging coal, harvesting barley or for that matter nursing my family through a smallpox epidemic in a peasant hut and watching my children die around me? No. In a single generation my family has become solidly middle class with all the values that entails. My father was born in a small hut in rural Slovakia, and through his own efforts has become reasonably well off and is has done a lot of charitable work lately, sharing his (modest) wealth in his old age with good causes.
I know this is getting way OT, but I'm just making a point that of course family background is important- but that royal families are not really any better or worse than any other. What's important is the values of the individual concerned.
I do agree that royals may be used to the spotlight, although not necessarily. How many papparazzi chase Theodora of Greece around these days? I wouldnt even recognize her if I saw her in the street, and I read royalty boards.
There's a lot more attention given to actressess and the like and "hollywood royalty", but I hardly think that there are many actresses who would really fit into a royal role comfortably.
And you are right, we don't want a Diana situation again. That's why William should marry someone he knows well, has a friendship with as well as a romance- someone he LIKES as well as is attracted to. But she doesn't need to be royal- just smart and adaptable.
Just my humble opinion of course.
