First, you're committing a very common error; you're looking at
absolute profits and not
profit margins. The oil industry is a volume business, they face extremely high fixed costs and make a relatively small profit margin from each transaction.
Sources:
http://money.cnn.com/2008/04/29/markets/thebuzz/
https://everydayecon.wordpress.com/2006/04/26/oil-profit-margins-vs-other-industries/
http://mjperry.blogspot.com/2011/05/oil-profit-margin-ranks-114-out-215.html
Basically, the "oil companies make excessive profits" meme is false because it looks at absolute profit rather than marginal profit. It also fails to note that a lot of what drives oil prices is not "corporate greed" but rather OPEC greed (the greed of the governments of oil-producing nations).
You aren't taking compliance costs into account. And the ludicrously complicated tax code makes these compliance costs (even those for tax avoidance (since accountants and lawyers cost money!)) somewhat substantial.
I'm all for competition but if you think that simple anti-trust will solve problems, you need to look at empirical reality.
First, the gambling market isn't a free market; it is a very tightly regulated market with massive entry and exit costs as well as licensing requirements etc etc. So simply applying basic "we assume perfect competition" economic theory to the gambling market will not work.
Second, Macau has lower house margins than Vegas and most people play table games there (Vegas is mostly slot-based). It also has an oligopoly of only 6 gaming providers with massive tax burdens. Macau is tougher (regulatory-and-tax-wise) than Vegas and AC; the American markets are freer AND have more competition! Yet Macau has lower aggregate house edges (although yes, granted, they have dumber gamblers who gamble a lot more).
In other words, consolidation doesn't necessarily negate the chance of getting good games.
Third, consolidation can in some cases LOWER costs. Its called Economies of Scale.
Fourth, you don't necessarily need active competition to lower costs; merely easy entry and exit to and from the market (Contestable Markets theory). Vegas is, compared to other gambling markets around the world, relatively contestable.
Fifth, its not as if Vegas lacks competition. Lets restrict ourselves to the Strip alone just for the purpose of the example... how many competitiors are on the Strip?
1) MGM
2) Caesars
3) Cosmopolitan
4) Wynn
5) Sands (Venelazzo)
6) Tropicana
7) Phil Ruffin (TI)
You are right that MGM and Caesars dominate the market but they clearly aren't a duopoly. There's more competition on the Vegas Strip alone than there is in all of Macau (and then, if we go beyond the Strip there are more players in the market... Penn National (M), Boyd, Station, Landry's (Golden Nugget) etc. etc).
In short, even if Antitrust might conceivably help (which itself is questionable), the market isn't sufficiently consolidated to justify Antitrust action in the first place (
and speaking as an economist, I don't approve of Antitrust in the first place).