Co-terms can graduate (or convert to grad status) anytime they complete 180 credits towards the undergrad degree, don’t have to wait until they complete +45 grad units. In fact most co-term students do convert to grad status at the earliest.
Don’t think Bing overseas is also the problem, all major universities have similar programs.
Back to OP’s question. There could be many reasons including :
- Higher percentage of athletes. They take longer to graduate
- Changing majors or deciding late on a major. (especially Engineering/CS) If you don’t start early right in the freshman year, it is going to be very difficult to complete an Engineering /CS major in 4 yrs.
- Poor pre-major advising (almost non existent at Stanford)
Regarding start ups, there are a few (hand full) undergrads leaving for startups, not enough to make a dent in the 4-6 yr graduating rate. A vast majority of the start-ups that come out of Stanford are started by professors and their grad students.