Vegas odds are also sometimes based on who they think will win.
Ever see a spread that just didnt look right and sure enough Vegas knew something that everyone missed? I have.
A lot of money can be made at the start of every of an NFL season because Vegas always has point spreads that are off base because they dont have the teams dialed in yet. Just watch.
The perfect scenario for Vegas isnt equal money on both sides, its the majority of the the publics money on the wrong team. The Rams were 13 point favorites to beat NE in SB36. How many folks took NE and the points? Ill surmise not the majority.
I always get into this type of debate on this board, and your statement is correct (the other "theory" is incorrect.)
If Vegas truly only cared about equal betting on both sides, they sure are doing a crummy job. If you look at the actual betting on these games, the bets are rarely close to 50% and usually at 70% or greater in favor of one team. Simply put, it's tough to predict momentum and betting trends, as public perception changes during the week. That is exactly why objectivity, computer simulations, and inside information is critical. Yes, Vegas may adjust lines a point or two to hedge their bets, but overall the money is made by projecting, as close as possible, a 50/50 bet.
Also, suppose that the Jacksonville Jaguars were playing the New York Giants. Vegas anticipates a gigantic amount of money bet on the Giants from the NY market, and to even the bets on both sides, they would need to adjust the real line (Giants -7) to try to attract equal betting (Giants -11). Don't you think sharp bettors would absolutely annihilate them? More likely, Vegas would move the real, prediction-based line to Giants -7.5 -8, a small change to hope to attract more balanced betting but a far cry from the type of strategy that many people claim they use.
So Vegas is never going to be "balanced" in the sense that they make a profit from the vig on every bet, and there are rarely games where they are going to win either way. Their goal is to win half the games and lose half the games (win where the majority is wrong, lose when the majority is right.) The difference is that when they lose, and the majority is right, they get a discount on the payout (the vig of 5-10%), while the bettor never gets that same discount. That's the real business model, folks.