1) The choke must handle large "magnetizing currents" as well as the DC current. That means it must have some magnetic headroom, so the same choke used later in a filter would have a higher current rating.
2) More subtly, at high AC flux the permeability of the iron is higher, so the inductance is more strongly dependent on the air gap - a precision air gap is needed.
3) Because of the large AC, the choke is under greater vibrational stress, both magnetostriction and simple magnetic attraction among any iron parts in or near the choke. So it has to be better built mechanically, with tighter bolts or channel frame, better varnish impregnation, etc. in order to prevent excess vibration.
