>... people were willing to pay for an a set of partially broken dishes if they were compared to an incomplete set than if they were sold alone...
I think this is similar to what is described by Dan Ariely in his book, Predictably Irrational, as the Decoy Effect. Relevant excerpt from Wikipedia [1]:
"People not only compare things, but also compare things that are easily comparable. For example, if given the following options for a honeymoon - Paris (with free breakfast), Rome (with free breakfast), and Rome (no breakfast included), most people would probably choose Rome with the free breakfast. The rationale is that it is easier to compare the two options for Rome than it is to compare Paris and Rome. Ariely also explains the role of the decoy effect (or asymmetric dominance effect) in the decision process. The decoy effect is the phenomenon whereby consumers will tend to have a specific change in preference between two options when also presented with a third option that is asymmetrically dominated. This effect is the "secret agent" in many decisions."
In your case the third choice - email - is the decoy or secret agent - making the other two options more attractive for ease of use.
I think this is similar to what is described by Dan Ariely in his book, Predictably Irrational, as the Decoy Effect. Relevant excerpt from Wikipedia [1]:
"People not only compare things, but also compare things that are easily comparable. For example, if given the following options for a honeymoon - Paris (with free breakfast), Rome (with free breakfast), and Rome (no breakfast included), most people would probably choose Rome with the free breakfast. The rationale is that it is easier to compare the two options for Rome than it is to compare Paris and Rome. Ariely also explains the role of the decoy effect (or asymmetric dominance effect) in the decision process. The decoy effect is the phenomenon whereby consumers will tend to have a specific change in preference between two options when also presented with a third option that is asymmetrically dominated. This effect is the "secret agent" in many decisions."
In your case the third choice - email - is the decoy or secret agent - making the other two options more attractive for ease of use.
[1] : http://en.wikipedia.org/wiki/Predictably_Irrational Edit: Wikipedia link