Vegas odds are built to promote betting. Baseballprospectus has generally pegged the team as low 80s wins since Fielder left the team. It is heavily regressed so that generally means 'in the playoff mix'. Last year they actually got over a 90% playoff odds at one point, it took a really huge collapse to not make it. A collapse largely caused by most of the lineup getting nagging injuries at the same time, not due to lack of talent. I believe the odds are generally set to promote even betting on both sides of the O/U. Basically, Vegas wants 50/50 split between over bets and under bets. They use a lot of the same statistical numbers everyone else does to get to their lines.