I get it in most of my games. I agree banning is a tactic to limit the by civs following the patronage path tp limit other civs making Diplomatic Victory that much easier.
In "my game" they can ban CS's all they want. I always have a hoard of cash by the late game, (35,000-50,000GP+) and I will not let another civ gain enough influence to win the Diplomatic Victory vote. Still, even 50K can run out while endlessly bribing CS's, so unfortunately, once DV becomes available the winning choices, realistically, are narrowed to Diplomatic Victory or Domination.
Thus, I see Diplomatic Victory as the easy cop out that Science Victory was in earlier editions of Civilization...not very satisfying but a quick way to end the game, when my early and mid game strategies fail to work brilliantly.
Nonetheless, while Diplomatic Victory is pretty lame, the diplomatic game through the World Council has become the first potential rival to military victory as a "complete" game experience...it's just not there yet. (I still haven't gotten fully immersed in the cultural game - I enjoy it in principle - but when I get to the point of trying to figure out that chart and "theming" I find it about as interesting to me as trying to read a printer manual).