There are 2 things..
First, the 1/3 rd stress increase for soil pressures shouldn't be taken for granted, and shall only be be used after due consultation with the geotechnical engineer. I dont have a code reference for 33% thing but if It isn't mentioned in the code, it is commonly allowed by the Geotech engineer. The following note is from the geotech report for a current project. "The net allowable bearing pressure may be increased by one-third for transient wind or seismic loads."
Second,
Another possible alternative would be to reduce forces and have a economical design ,
The 25% reduction applied to the overall overturning moment at the base of the structure due to lateral seismic forces (talking about the big picture here - not moment on an individual footing). As the structure overturning moment is generally resolved into a force couple in braced frames or individual moments in footings, I read this as allowing a reduction in either the force couple or the individual moments for design, both strength and stability, of the footings.
As basis see the 2009 NEHRP Provisions which basically provide a commentary to ASCE 7-2005 (downloadable - big file - here: http://www.fema.gov/...cord.do?id=4103) which says for this provision (emphasis added):
C12.13.4 Reduction of Foundation Overturning. Since the vertical distribution of forces prescribed for use with the
equivalent lateral force procedure is intended to envelope story shears, overturning moments are exaggerated. (See
Section C12.13.3.) Such moments will be lower where multiple modes respond, so a 25 percent reduction is permitted for
design (strength and stability) of the foundation using this procedure.
Note:This 25% reduction is for seismic only.