I've seen the tactic before. Create a sense of urgency through scarcity. Scarcity makes people buy.
Seriously? Limited quantities of a digital asset?
Having seen most marketing tricks (starting with the best one of all - "lather, rise and... repeat") I may be a little too sensitive to it.
But I hadn't considered that there are sites that use this tactic even to sell eBooks or subscriptions, so I should probably clarify this… Curious to know if other people got the joke or took it literally?