y do they have bandages? same reason fotball palyers put that black stuff under thier eyes......looks kool, makes them look tough, etc.

plus also the injury thing....remember sasuke stabbed himself in his quads when oro gave him that "look of death"......with the bandages already there, the doesn't need to wrap it again.

and also, in a battle, the enemy would most likely hit u there in order to try and stop ur movement.....below ur knee is mainly bone (on the front side atleast) and plus its harder to hit cuz its thinner