The impression I get from the anime I watch is that -sama, besides being a
very high honorific (i.e. something you'd say to a high-up superior) can,
when used by a woman to a man, also be a sort of endearment.  Sort of like
saying "You are the lord of *MY* universe."  This is how Aeka uses it to
Tenchi, how Kodachi uses it to Ranma.  (Hmm, now that I think about it,
*all* the "relationships" I know of where the woman uses -sama are
one-sided.)