I don't personally gamble nor do I advocate it, but I always find over/unders fascinating.
For the uninitiated, over/unders are a simple bet. The book throws out a number of wins for a team, and you place your money on whether you think that team will win more or fewer games than the target number. Remember that Vegas is not necessarily predicting that these are the records teams will finish with. They are trying to encourage an equal number of best on both sides.
That means that they are weighing not only actual team strength but public perception of that team as well as the popularity and optimism of the fan base.
The Houston Texans' over/under is 10 wins
That's basically right on the number I would predict for them as well. What makes the Texans tough to call is the injury situation. Fans are optimistic right now, but they have several aging skill players who have struggled with injuries.
I would argue the team is less equipped than ever to handle losing Matt Schaub or Andre Johnson. If everyone stays upright all year, 10 wins might be a little conservative. But if one or both go down, I can see the Texans stumbling.
The Tennessee Titans' over/under is seven wins
This is shocker to me, as I have them down for 10. In fact, I can't see them winning fewer than five games. I suspect that Vegas is bearish on the Titans' draft and uncertain quarterback situation. Instability tends to lead to suppressed win totals.
Unless you think the Colts and Jaguars have significantly improved, this is a value. They have some winnable games at home, and while they may not make the playoffs, I think they win at least the seven games necessary for a push, if not more.
I think this number is close to perfect for both teams. I had the Colts at four wins before the draft, but now think five is at least possible, though a tad optimistic. The Jaguars I have down for six victories.
These teams illustrate the fact that public confidence plays into the line. The Colts are more of a 'public team' than the Jaguars thanks to the nation-wide popularity of Peyton Manning. He's gone, but Andrew Luck inspires more fan confidence than Blaine Gabbert. While I think the Colts are a shade overvalued here, neither team's line is far enough off to represent a true value.
Gambling is a losing game, and these lines illustrate why. Vegas does its homework and rarely gets beat. They have the AFC South close to nailed, and haven't offered much opportunity for the squares to score.