I suspect quite a few emails were sent to friends and family saying "Log on to the following link and get free Gold membership to Flying Club", using the link as posted by Edison on the first page, that link had NO T&C's:
This campaign appeared on AFF very late in the piece, so while anyone who read it hear would have seen the T&C's in the first post of the thread, the viral effect could have well resulted in many customers not being aware of the terms and conditions if they were made aware of the offer by other means, which is why Virgin prefaced their email with "You recently applied for Instant Flying Club Gold membership through an unofficial online channel. As a result, you were not made aware of the terms and conditions or criteria to qualify for the offer."