It doesn't feel like it's a fair fight otherwise, since it means he's exploiting a weakness intrinsic to his competitors
Late in the first round you can see Jennings change his strategy a bit -- he starts ringing in before he knows the answer. Jennings is exploiting the fact that Watson won't ring in until it has confidence in an answer.
That's awesome. He can make that strategy pay off because he's Ken freaking Jennings. Usually the money penalty for buzzing in but answering incorrectly (or not at all) would dissuade a contestant from buzzing in before actually knowing the answer.
Late in the first round you can see Jennings change his strategy a bit -- he starts ringing in before he knows the answer. Jennings is exploiting the fact that Watson won't ring in until it has confidence in an answer.