It’s an amazing achievement, this is way up the difficulty scale from playing chess (or tic-tac-toe for those that remember Wargames).
I think a few things are probably working for them here though
1) Jeopardy questions are fairly short, they have to fit in those small boxes so there’s unlikely to be a ton of extra words or descriptors. Questions are going to be straight forward for the most part.
2) They have a huge number of questions to run the program against from all the previous shows. So Watson’s “team” can run their program against thousands of questions, see what types of questions they get right or wrong, and then add to their solving algorithm as needed and run everything again very quickly. At the start they were probably making huge changes every day to try and get the percentage of right answers up. Eventually they cover a wide variety of not only topics and categories but styles of questions.
3) There’s not much penalty for not knowing the answer, worst case scenario is someone else gets it, they don’t have to guess at questions they aren’t sure about.
4) Fast computers = fast answers and fast buzzing in. If Watson “knows” the answer, it probably has it way before us poor meatbags.