If I'm not mistaken, in most states, the only thing really "divided" up at the end of the marriage are the assets created IN the marriage. I know when my parents got divorced, even though it never went before a judge, there was never any question that my Dad was NEVER getting a dime of my mother's money from her family.
The only times I've seen a legitimate reason for prenups is if there are children coming into the marriage that weren't born to the couple IN the marriage. Most of these consisted of "And I will not be responsible for little Jimmy's private school if we get divorced, because he ain't mine!". Or if there's a lump sum offering in case of divorce, in which case it becomes a business proposition, not a marriage, IMHO.
I guess this is one reason why I haven't gotten remarried in the 19 years I've been divorced - I'm not a big fan of all the rules and regulations people set up BEFORE the marriage in regards to the DIVORCE.