Well, I'm being unfair if I implied that DO schools cover all the big picture stuff. Sometimes I wonder if they know what board they're referring to when they say, "oh this here is board relevant."
Anyhow, for accreditation, the schools must show that they provide a minimum number of hours of "asses in lecture seat" time (credit hours) and how/what they plan on going over during those hours. It's covered in painstaking detail in each class's syllabus. In many of my system based classes, we have time blocked out for "independent study" for a specific class. I asked about this (because I thought it seemed silly) and was told that those independent study hours counted towards the credit hour criteria. Perhaps the PBL programs are similar?
Logic-wise, I understand where you started. But, how could the ACGME let in students to their programs if they spent less time on material? If that were the case, anyone could just take the USMLE and, assuming their board scores were sufficient, apply to ACGME residencies. I know the LCME would be pissed.
Anyhow, the AOA/COCA have to demonstrate through their accreditation process that their schools provide equivalent education (via credit hours) to LCME schools. Imagine the $hitstorm it would cause if osteopathic schools really did somehow spend 200 less hours teaching basic science material and replaced it with largely untested folk medicine?

I'm not going to lie, that would be kinda awesome!