Hah! I should have read this before:
The article itself is not very scientific in some parts. It relates to the study that says that writing is good only if you are writing about a bad experience, but bad if you aren't (also from Scientific American, but you'll need to pay for it to read it - appeared on Scientific American Mind, August/September 2007), but it seems like they don't seem to reference it for some reason. If SciAm was a scientific journal, the editor wouldn't allow this to happen.
Independent on missing references, it's still an interesting reason to convince people to write! Maybe:
"[...] blogging might trigger dopamine release, similar to stimulants like music, running and looking at art."
Ah... I feel so much better right now! :-)