The pricing model could be the logical conclusion to some basic behavioural economics insights. Feeling of a loss >> feeling of a win. Thus you create an ever present feeling of that potential loss (missing out on the lower price) which forces potential buyers to act to lessen that feeling of possible pain as opposed to the standard approach of selling based on the feeling of a win (my nice and shiny logo). This idea could probably also be leveraged to combat procrastination somehow. It also has that novelty factor of the pay per pixel advertising from back in the day. Neat :)

I guess the only problem is that the last logo shouldn't sell easily (without adding more).