Why are unique labels for price fields required?

This is a question not a proposal or bug report. Should a unique label for price fields be enforced (seen attached)?

Here are two use cases:

• event registration where the price of attendance changes over time (early bird) but the event itself or the nature of the registration doesn't change

• membership registration 'special' where prior to a certain date memberships are on sale

It seems in these cases a unique label is not necessary.