As a working diagnostic radiologist in a busy private practice serving several hospitals, this has been my experience as well.

We have some excellent ER physicians, and several who are very good at looking at their own xrays. They also have the benefit of directly examining the patient, "it hurts HERE", while I am in my basement. Several times a year they catch something I miss!

But when it comes to the hard stuff, and particularly cross-sectional imaging, they are simply not trained for it.