OK - re-read my comment with the word 'unsolicited' removed.
It is still unreasonable to send out legal threats because you did not receive a response from an email. You don't know if the email was read, or if it was even delivered to the user's inbox (it could have been flagged as spam, for instance). Or, as it appears to be in this case, it could have a poorly worded and misleading subject, causing it to be ignored.
Furthermore, did you read the email that was actually ignored? It is linked in the article, and located here: https://gist.github.com/1833289
Note that it specifically says that "if you agree to this arrangement" to implement the link back. There is actually nothing in that email that would suggest that any action was required; the next step sans link back was simply for Gigya to then send a price quote.
While I am not suggesting that the alternatives offered are or are not fair or reasonable, the follow up email did its job in getting the service consumer's attention and more importantly action in regards to the matter.
Well, naturally. I was not arguing that being unreasonable was not effective in forcing action on someone's part. I would argue, however, that it is unethical and counterproductive.