Well, it looks like you're just using anecdotal evidence. If you want some anecdotal evidence, whether high school kids get into the top perceived undergrad schools really just depends on how much their parents push them. Virtually all of my parents' friends/acquaintences' kids got into Ivies or at worst a Johns Hopkins. What do all those kids have in common? Overbearing parents when it comes to education. It's easier to become the "top of the top," as bakfed said, when someone is driving a rocket under your butt and 90% of your competitors, i.e. normal American kids, have parents more concerned if you win your next football game or too busy dropping out (1/4 national HS dropout rate). American kids that actually care about shooting for those top schools have it made when you look at just about every Asian country's education system for instance. I shudder to think what life would have been like if I grew in another country and had to compete to get into the IITs or Tsinghua/Peking/Todai.
I know enough people that went to the UC schools to know it is significantly easier to get into as in-state, and no, you don't have to be necessarily top Ivy material.