These cases aren't similar.
One involves a consumer complaint board where customers of a business related their [presumably real] negative experiences with a business. The other involves a local news commentary forum where one or more individuals engaged in a campaign of obscene and libellous commentary about an individual.
To my mind [again, I'm not a lawyer], the former is not actionable while the latter clearly is. I'm not surprised that the subpoena in the Video Professor case was quashed. If there were a reasonable suspicion that the posters to the complaints forum were making false statements, then it might have held up.
See a discussion of Federal case law on this subject here:
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cyber.law.harvard.edu/st ··· net.html