Sorry but I will never be convinced that on average someone who received their undergraduate degree from Harvard will have the same life experiences than someone who went to a state school. For one, state schools usually have a much larger student body. Hence, statistically, your odds of interacting with individuals of different socioeconomic status, ethnicity, and interests are inevitably higher. Cultural competence and social awareness, two very important qualities in physicians, come from these sort of interactions. The more exposed you are to such individuals, the more likely you will be to relate to/with them. That is specifically why it's highly valued for applicants to have some foreign life experience; by living or spending time in other countries, it obviously shows that you can appreciate differences; hence, you gain cultural competence.
Now if you attend a small Ivy-League undergraduate school, I don't see how diverse the student body can be. You literally had to be flawless during high school to receive that admission. Of course there are your usual outliers, but on average I think the student body will be pretty predictable: overly-zealous students who busted their ass in high school (but props to them for getting into Harvard). It's difficult to find a healthy balance between academics and a social life when you're nearly academically perfect. YES, THERE WILL BE YOUR EXCEPTIONS, but on average, it's quite difficult to have flawless academic credentials and your fair share of partying, etc. I am not praising social gatherings, but the level of social activity that takes place in these events are unparalleled.
Now, most MDs at Harvard, have done well in school for a while now. They have always taken it very seriously and although undergraduate is a joke for some, it's very hard to score a 40, have a 4.0, do 3 years of research, be superman, and still have a fair share of college fun. YES THERE ARE EXCEPTIONS, but most can't handle both scenes (also, sports at Harvard cannot be compared to the SEC, ACC, and Pac-10). Furthermore, this process has slowly been taking place since high school. These individuals continuously deprive themselves of normal adolescence and college life to earn those steller credentials. I am not really hating on it but it has to be acknowledged.
And the earlier you start the easier it will be down the road. If you've been hanging out a lot since high school, it sort of becomes your little niche. You become comfortable going out and meeting new people. The younger you are, the more naive you are and the more likely you will be to accept something. You aren't as reluctant and approach things with the slightest hesitance. You probably will make some mistakes here and there, but good judgment comes from bad judgment. In that perspective, I think social activity is comparable to sports; the earlier you start, the better. Personally, I believe that on average all these Undergrad superstars at Ivy-League institutions that eventually go on to Harvard Med and etc, don't fit that population pool and miss out on a ton of experiences that may not have seemed valuable at the time, but will surely facilitate patient/doctor interactions. It is never too late to start, but you'll never have the swagger and confidence of someone who has years of experience. Kind of like clubbing, if you didn't start at a young age, it's going to be difficult to haaaaaaaaang...
And all my comments about 40+ scores come from personal experience. I interviewed at 10 different schools, including some of the best. The applicants I met were EXTREMELY COCKY and cliquish; when Harvard applicants ran into Harvard alumni, it was like OMG, LEMME SUCK YOUR D!CK. Seriously, get over it...
Sorry if I'm picking on Harvard but the interactions I had with some of their applicants, were the least pleasant. Hey, but who cares if they were cocky, socially inept fools, right? They scored 40+ on their MCAT! It seemed like all these dudes wanted to know was where else I interviewed at and if they happened to be rejected at that particular school, my stats, including GPA and MCAT, were always questioned[b/].