Illustrating that the computer has the advantage over humans is the entire point. Competitive game play is not about 'fair,' in fact, the best players specifically try to make the game as unfair as possible, within the rules of the game.
• receives question (and answers) as coded text, rather than having to sight-read or listen to them
• no audio/video clues
• no categories that require an extra Trebek-explanation
It may even be receiving a direct signal when it's OK to ring in, rather than assessing Trebek's cadence and the same light-indicator as the human contestants rely upon.
So other 'balancing' changes shouldn't be out of the question.
I particularly like the idea that the penalty for a moment-too-early buzzing could be eliminated, and/or treating all buzzes in a small window around the traditional earliest-allowed moment as simultaneous. That still rewards quickness, without heavily advantaging the computer's ability to perfectly synchronize with the buzzing-period.
Once two buzzes are considered simultaneous, the contestant chosen to answer could rotate in round-robin fashion, or (for maximum drama) be the one furthest behind.
Presumably a human could consistently beat Watson to the buzzer by predicting when the light would go on.
There's a lock-out that applies if you buzz too early, and the variance of the 'beats' between Trebek's finish and the light, if that's a human-mediated process, may be far larger than Watson's light-fired reaction time.
The point being that at the highest levels of play, all of the contestants know most of the answers. This is a very important thing to remember. It means that even in all-human games, it's not "do you know the answer" but "can you ring in fast enough."
So it still is really quite impressive that reaction time matters at all to Watson, because it implies that it can compete at the highest levels.