In my last game (where seemingly everyone declared war on me, yet in doing so, saying they didn't like their chances but they felt they had no choice or whatever) I wasn't able to get any tribute despite having the most powerful military in the game. Having that AND taking over cities? Still no bribe to end the war.
Ah, true, sometimes you have enemies who are determined to fight you to the bitter end, even when the last city you left them with is a 1 tile island. That's not actually because of stinginess though, it's because of holding a grudge. I'm not sure how to feel about that one. Annoying, perhaps, but pretty realistic for it to happen sometimes. And it's not like they pose a real threat. Still, you can't help thinking "I cannot believe these idiots" -.-