Why a static port?

I can understand why pressurized aircraft need static ports,
but why do unpressurized airplanes have them? I wouldn't think
the pressure difference between the inside and the outside of
the airplane wouldn't differ by that much. (When I open the alternate
static port in my C185, the altimeter changes by just a couple
of feet.)

Without the static ports, we could get rid of all that silly
tubing and just leave the static port connection to the instruments
open to the air. (Of course there is no getting around needing
a tube for the pitot port.)

~Paul Mennen