Other than to admire the few freakish linemen who clear the 40 yard dash with LB like numbers, there is nothing particularly eye opening in learning about the 40 times of linemen. However, to get to 40 yards you must run 10 yards first. That 10 yard split, however is extremely useful for guaging the quickness of linemen. If they have to run 30 more yards, well, maybe we can learn what kind of shape they kept themselves.
So yeah, for me I don't see the big deal in asking the big guys to run the 40.