Dave,
There is a big difference between the current flowing on
the inside of the shield of coax and any current flowing on
the outside of the shield. The current flowing on the inside
of the coax shield is the same current that flows in the
center conductor (not the same polarity/phase). Ideally, there
will be no current flowing on the outside of the coax shield,
but you very seldom ever run across the 'ideal' situation. The
current flowing on the outside of the shield is what makes the
feed line radiate.
'Doc