Well, the thing about Radiology is that you deal w/ other MD's, you're have relationships w/ the patients. Primary care & surgeons have personal relationships w/ their patients, thus, patients expect 'their' MD to be there when they go into the office. Patients don't even know the radiologist who read their study, 1/2 the time don't even know what a radiologist is.
That sounds like it sucks to be a Rads (no warm & fuzzy relationships), but it really is a blessing in disguise. That allows Radiologist to take all kinds of vacation as long as another Rads is there to read the studies, doesn't matter who reads it as long as it gets done.
A primary care/surgeon can't take vacation like that b/c that will break the 'continuity of care' for the patient. Patients hate when they go to see their MD, only to find that they're on vacation & another MD who doesn't know them is covering.