I have begun to think the same thing. I especially got suspicious when he would behave as if he was unsure and then quickly spit out the correct answer.
Something just feels wrong about this. I would be less suspicious if he missed a few more since the categories are so diverse. When things seem too good to be true, they often are.
If I was a contestant and had to compete with him, I'd figure there was nothing to lose by sitting on the buzzer and give myself a fighting chance. If you assume you are going to lose, go for broke.
I'm glad I'm not the only one. We're watching Jeopardy every night now, just so we won't miss it when he finally loses.