Experience levels and abilities vary flaps but in general the landing pilot given a clearance only registers that and not the wind figure that was passed. Concentration on the final stages of landing means many pilots shut down hearing in proportion to how demanding they are finding the task.
This is a simple and safe demonstration of the effect The Magus describes in the main body of his post.
This is entirely normal human behaviour - just ask your partner a simple, utterly banal question when they're concentrating on a technical task and note if you have to repeat it. The questioning technique is just a very simple but very effective tool in our armoury to assess a colleague's position in a constantly shifting situation.
Rob