it is entirely a true statement.
why would height matter to a snow board. it is on the ground and is interacting with the underside of your feet... so why woudl it care for how far above your hair happens to be?
weight is important because when we consider board length, what is more precise, is to say we are considering board AREA; or in other words, how much area a board gives, to distribute your body mass.
as i am sure you know (but just in case)... when on soft stuff like snow, if you stand on one foot, you will sink. if you stand on a big old board tho, you will 'float'.
it is this fundamental law of physics that causes us to worry about rider weight when choosing the best board length. c'est facile non?
