I'm not saying this is some novel realization, but the one day the
thought popped into my head.  I just searched (
http://duckduckgo.com/?q=grangerfords+%26+shepherdsons+civil+war ) and
it looks like this is a relatively common interpretation.  I think it
adds another level though, and makes me want to reread that section of
Huck Finn with the civil war at the forefront of my mind.  It also
adds another layer of sorrow to when Huck finds Buck dead (brothers
killing brothers).
-Andrew