Tom,
When the Schooner "America" raced the best the British had around the Isle of Wright in 1851, the members of the New York Yacht Club took that Trophy home, and dedicated it to international yacht racing.
From Wikipedia:
"Any yacht club that meets the requirements specified in the Deed of Gift has the right to challenge the yacht club that holds the Cup. If the challenging club wins the match, it gains stewardship of the cup.
....
The trophy was held by the NYYC from 1857 (when the syndicate that won the Cup donated the trophy to the club) until 1983 when the Cup was won by the Royal Perth Yacht Club, represented by the yacht Australia II, ending the longest winning streak in the history of sport.[2]
From the first defense of the Cup in 1870 through the twentieth defense in 1967, there was always only one challenger. In 1970, for the first time, there were multiple challengers, so the NYYC agreed that the challengers could run a selection series with the winner becoming the official challenger and competing against the defender in the America's Cup match. Since 1983, Louis Vuitton has sponsored the Louis Vuitton Cup as a prize for the winner of the challenger selection series."
The two boats racing in a round robin series to race the holder of the cup--in this case "Oracle" are doing what is called "match racing". There are a number of tactics which may not be apparent to the casual observer, but it involves a lot of stategy and tactics--but was much more apparent in the slower older mono hull boats. It happens so fast that even the comentators missed the fouls yesterday when Artemis fouled Luna Rosa. That ended in two penalities--basically the penalized boat had to give up a boat lenght. The second penality was because Artemis didn't do the first one fast enough and gained an "unfair" advantage. The other two were technical--one by going a few meters off the imigery line of the bounds of the course, the other involved movement of the trimming boards on the boat.
In Match racing, the boats may not cross the starting line for a minute--it is all about tactics and blocking the other boat. This happened yesterday--and even though Artemis got the advantage, they committed a foul, and lost first leg of the race. From there on it was mostly speed..
I agree with Tom, that it looks as if there are just two boats going back and forth. The reason for the specific course is that is because these boats have to stay in certain bounds--they do not do well going right into the wind or right down wind. The current, wind shift, wind shadows, etc are all taken into effect. Of course today, there are 30,000 pieces of information a second taken into account on computers both on shore and aboard. For example the wind velocity and direction is measured ahead of the boat with laser monitors on the boat.