In my opinion, you're correct. The physiological malfunction may require a lifetime of pills to keep it in check. The physiological would also include the bi-polar manic-depressives. The situational depression may require pills long enough for the situation to be managed, however that may be done. And when there is clinical depression with situational on top of it, there is definitely the need for medication to enable the sufferer to handle day to day life.
In all these cases I believe that "talk therapy" with a therapist or counselor should accompany the medication. There are tremendous benefits in learning new coping behaviors, etc., that can really help. I believe this is especially true of situational depression, caused by grief or divorce or other events. Having someone to talk it through with can be quite useful.