Regardless, after your first year, no matter what program or specialty, 28 hour calls become the norm. As a second year surgery resident for example, you can plan on taking a 28 hour call two or three times a week. This is just how it is. For two main reasons:
1) There are not enough of us for everyone to get 8 hours of sleep a night. People can debate why or ways we should fix this, whether it's widening scope of practice for nurse practitioners or decreasing our pay so there is more of us, but logistically there are not enough residents to keep everyone well rested.
2) There is physiological relevance to a 24 hour cycle in many diseases. For example, if a patient comes in with a bowel obstruction, the process of observation, lab evaluation, imaging, +\- surgery takes sometimes 24 hours. 12 is sometimes not enough to appreciate the full evolution of acute disease.
Big topic here. My experience is anecdotal and limited. Why they did a big study to see what was best. Still, it only applies to first years.