Hmm, even at my most cynical I would say the difference is the free conference is a much smaller (and thus presumably less effective) bribe. Giving away tickets to a conference which they sell the tickets for costs AMZN very little (sure, there are costs associated with putting it on, but those would have had to be paid anyhow, adding an attendee or two won't change much). So it's a few grand worth of airplane tickets vs. $700K...