Hmmm...maybe its different where you're at...but I've never had an IM guy do post-op management on my patients. We manage the hypertension, hypothyroidism, diabetes, chronic arrythmias, pain, nutrition, etc. We do consult medicine specialists for problems in surgical patients better managed by those specialists (renal failure needing dialysis; pancytopenia, new onset arrythmias, etc.).
While an IM physician may "make the diagnosis", often I find they don't, don't want to or get a surgical consult to cover themselves (I cannot count the number of times I've gotten a late night consult on a patient with a KUB result of "ileus"). Why should they? They're not surgeons and aren't trained to make surgical diagnoses just as we aren't trained to do IM diagnoses.
Surgeons don't train any longer than any of the IM specialists with fellowship training, so I'm not sure that has to do with a desire to not rely on anyone else and their attitudes but rather the type of person who is often attracted to surgery. Many surgeons I know will openly admit that they are not the smartest physicians in the hospital but defer to the nephrologists, critical care intensivists and ID as the brightest.