It's all about having enough breadth that the other bits of information presented can help whittle down answers by way of association and relationships. Good trivia players rely quite a bit on intuition.
Ken Jennings mentioned (in his book) how Jeopardy! often has questions about rivers, so it was a fairly simple matter to just memorize river names and some basic associations with which to answer questions.
It seems like Watson is mostly a really sophisticated algorithm on top of lots of brute force (2880 processors?!). Though I guess it could also be said that humans are just ugly bags of mostly water.
That said: in something like medicine (differential diagnoses), such a system could also be extremely useful, given the frequent occurrence of a fairly limited number of "answers".