I sent an email to saf.org, basically asking them WTF. I'm a SAF member, so maybe I'll get a reply.
GRC donations are not tax deductible and SAF donations are. So there will be different rules about what electioneering they can do; GRC does not have to worry about losing its tax exempt status. That's probably the whole thing. (there ought to be a statement to that affect on both web sites)