Princeton has a big focus on paying attention to undergrads (
e.g. see here).
I went to a small liberal arts college and see the huge benefit that I got by going there. The concept of taking summer classes because you can't get the spring section you need for your major is non-existent (this is presumably true at big places like Harvard, too).
Really, IMO, it's obscene to force students to pay $35K per year and then expect them to shell out another $6-8K* for summer school because all the sections of Chem 102 were full in the spring, and you'll end up staying an extra year if you don't take this course ASAP.
*My estimate for costs of tuition and fees, plus rent if you could be living at home for free, plus lost wages assuming 20 hours per week at $12 an hour lost (this would be more if you have a higher-paying job like lifeguarding or writing code).
So these costs would have to be added to the in-state public university cost at schools where the need for summer school is common (e.g. anywhere in California). Add a fifth year (very common) and a sixth year (common enough) and you could end up paying almost as much for that California public flagship as you would have for Williams: $35K * 5 years = $175K (assuming no inflation; yeah, right), and we haven't added in summer school yet.
