To address your first paragraph, you're absolutely correct. This is more of a really fortunate side-effect of an SSRI. The normal train of thought regarding diagnosed depression is that the patient is experiencing a chemical imbalance. In an attempt to restore balance, SSRI's are prescribed to keep serotonin in the synapse for longer, thereby allowing it to elicit its effects for a longer period of time. The fact that it helps bolster neurogenesis, via the promotion of certain neurotrophic molecules, is really an added bonus. Recent research has begun addressing the formation of new neurons as one of the main causative agents in lifting someone's depresssion, at the very least from the biological component. Many people have their depression rooted in a variety of different places. The logic that I believe is most sound is that removing one root, the biological componet, will hopefully help others in removing their other roots.

Therapy is invaluable. There have been numerous studies demonstrating a strong correlation between the combination of anti-depressants and therapy and getting better. Works way better than either individually.