I agree with you...this happens in the Navy alot also, a reserve member temporally becomes an active Duty member to attend school. When I was an Instructor, I had several students in my SONAR schools who became active duty to attend them.
I haven't read all the posts, but as a former ARNG Cmdr. they are correct about W not being in the Active USAF. NGs are sent Active Duty Training, their prefexis remain NG. We use to tell the NG recruits that they could become regular Army after their NG service if there was a national call up. The reasoning was that they never actually served in the Army. Their 6 years of service still left them open to a recall. (or the draft at that time)
This 26 year old campaign brochure listing service in the Air Force is in error, just like the statement that says he finished his Harvard MBA before entering the Guard. That is the best way to address it, as an error made by campaign staff. Kerry should be understanding how this happens, his staff listed him as the co-chair for the Senate Intelligence Committee on their website. One small problem, that was Bob Kerrey.
If the Bush campaign wants defend the story of the President being in the Air Force (unwise in my opinion) they can detail his active duty time for UPT at Moody AFB. I don't think that is a wise idea since your component doesn't change just because you went to school.