Someone that pays extra for the translucent floppy disks feels they are getting their money's worth. The utility per dollar they are getting out of translucent disks with a cardbord box exceeds the utility per dollar they feel they would get if they got translucent disks in a nice plastic case. This is why Andukar noticed people bought fancy disks but didn't get the fancy case too. They figured they already had a good enough case or didn't plan to use the case, so they perceved the value of the plastic case wasn't worth it.
The customer's preference can be seen as a utility function which would show the person's perception of the amount of utility that would be attained from using a good. For more information, look into a microeconomics book about the Theory of Consumer Behavior and Demand Analysis.
This has been an attempt to answer the question posed in the title of the node. Thank you.