Here we go again...the IIHS is lauded as The Voice Of God when it comes to vehicle safety. Well, they're not. And you guys have figured out some of it.
The offset crash test is new, for one. Heavy offset crashes are fairly rare in real life compared to the other numerous kinds of crashes out there. The fact is, all of those "Five Star Safety Rated" vehicles that pass these tests with flying colors are engineered to pass the test. So when they all start to achieve good scores...the IIHS moves the target again so they stay relevant. While I will concede they have contributed to some advances in vehicle safety, they (and the head of it) are very press-happy. The more press they get, the happier they are. Remember when they crashed the '59 Impala? That was simply to get more air time.
I work in the industry that funds this 'institute'. I once sat through a meeting where (I think it was) Dr. Lund espoused that driver training had no positive impact on safety. His view was that drivers will always be morons, so the car has to do the job for them. As a person who teaches advanced and teen driving, a racer, and someone who has avoided accidents because of my own training, I found his comments idiotic and insulting.
Crash tests should be viewed with the same weight and skepticism as a CarFax report. It's a tool for your toolbox, but should not be accepted verbatim as Holy Scripture.