A few thoughts:
1) This is becoming less of an issue for EM as radiology groups in most places - although certainly not all - are forced to provide 24/7 coverage to keep their contracts. As mentioned, this varies from complete coverage to just cross-sectional imaging. Again, as mentioned most places that typically exclude plain films are willing to read one on occasion. Either they want to keep the "nighthawk" contract as well or they are part of the group and don't want to deal with a bad miss by EM in the morning.
2) Radiology is vastly easier if you have access to the patient. It is also far easier if you are asking a single, relatively simple question. Example: we generally are acceptable at seeing blood on a head ct, but I am probably not going to look for or care about a small pineal cyst. I might be able to see concerning signs about the appendix, but I am definitely not going to see subtle, chronic lung pathology on a scout image.
3) Some things are subtle: my last month I didn't see a subtle spiral wrist fracture in a 9 year old that radiology found. I also knew that there was a relatively good chance that would happen. There are also things that a 10 year old can see, literally. Once we had a head ct of someone with a GBM on a monitor, a kid passing by in the hall said "that's bad!" Yeah kid, radiology, and a half-dozen specialties aren't going to end up adding much more, even thought they will add a lot more technical phrases
4) Even with radiology most physicians look at the imaging. It is rare, but switching left/right is still one of the more common of those errors, and perception errors (that even we catch) do occur. It also gives you a general sense of things: if someone comes in with abdominal pain and nothing seems too concerning on exam, and the ct looks textbook-normal to me, it is unlikely that they will crash due to abdominal pathology in the next hour.
5) A lot depends on your radiology coverage. We have very good coverage w/ very good turnaround times. So it doesn't depend that much on what we see; on the other hand if you are at a place w/ 2 hour turnaround times, a lot more will depend on you.