As to his final bet, it was the only move he could make. I also thought it was odd, but read an explanation this morning that made it clear.
He knew that she'd bet enough to shut him out (because she could), so he bet to make sure that the third place guy didn't overtake him. This way, if Emma got the question wrong, he would still win, regardless of what the third guy did. If she answered the question correct, which she did, there was nothing James could do at this point. So, in essence, he bet to take his response out of the equation. Pretty savvy betting, in my opinion.
And, for what it's worth, the "accidental" leak of the result probably helped their ratings, since some of the regular viewers (me included) were losing interest in seeing the game decided before the individual interviews half way through the first round!
Yep, James was hoist with his own petard. His usual method of winning was to poach all the big $ questions where the Daily Doubles reside, leaving the two challengers scraping for the small money leftovers. This time it happened to James. While I was kind of sad to see James go before he could clear $3 mil, I was rooting for Emma. I, too was getting tired of watching James win so effortlessly. FWIW, Emma has a similar cold-blooded/no personality style like James. She may stay for awhile.