> not all clinical depression is fully treatable by exercise;

We can expand this: exercise is moderately better than nothing to treat depression, unless you use good quality studies in which case we don't know if it's better than nothing or not.

http://www.cochrane.org/CD004366/DEPRESSN_exercise-for-depre...

> Exercise is moderately more effective than no therapy for reducing symptoms of depression.

[...]

> The reviewers also note that when only high-quality studies were included, the difference between exercise and no therapy is less conclusive.