Moving the line is the oddsmaker's effort to balance betting action, and often times such moves can have a major impact on a bettor's decision.
This has nothing to do with "oh, who will win the AL East" but rather where is all the money being put down. For example, if the Sox were 12/1 to win the WS, but there's a huge influx of betting on that line, the odds makers will reduce it to 10/1 or even further. However, if no one is betting on the Sox at 12/1 they'll increase the odds to 14/1 or wherever. It's about the casinos hedging their bets and knowing historically where people are putting their money. The onfield moves are secondary at best.
But I just don't know what I'm talking about I guess.
Welcome to the world of gambling, you must be new here.