The best code I have seen which clearly describes when and where to use a live load reduction is the IBC 2000.
Under section 1607.9.2 "Alternate floor live load reduction" it states "Such reductions shall apply to slab systems, beams, girders, columns, piers, WALLS, and foundations."
The code further states the exact formulas to use when taking live load reductions for the above structural elements. Their is a 60% maximum reduction for vertical members, which is more of a reduction than the standard 40%.
Hope this helps