I've only really read about Obama/Wright(or Ayers) and McCain/Keating.

The Obama case is about what Obama believes.  Wright and Ayers are both radical leftists in their politics.  If sharing a belief in radical leftist political figures is an indication of one's own political leanings, it is very relevant.   If the experience with Wright helped shape Obama's political ideology, why would we not take that into account?

On the other hand, McCain/Keating is also very relevant - it is about what McCain has done.  The question I ask is "What did you learn and how have you changed?"  In the case of McCain, it was his dealings with Keating that was the trigger for his strong political beliefs and actions on campaign finance reform and governmental deregulation.  He (in an article I read not too long ago) said that he did nothing wrong(illegal), but that brush with Keating was a "light bulb moment" (my term).  In that moment, his ideology was formed.  If the experience with Keating helped to shape McCain's political ideology, why would we not take that into account?

The difference between Obama and McCain?  Obama says, "that's not the guy I knew" (as if he could sit in the guy's church for 20 years and not know...AND write about the political beliefs of Wright and not know about them).

McCain says, "it looked wrong, I should not have done it and because of my experience I'm going to work toward fixing the system.

It's not about "GBA".  It's about what formed the political ideologies, how close are the ideologies of the student to the ideologies of the mentor (which is how Obama has described Wright).

It is about "what have you learned and how have you changed?"

McCain has told us and shown us.  If Obama sat in Wright's church for 20 years and cannot tell us what he has learned and how it has changed him...that says volumes about Obama.