LAS VEGAS—This city has seen more political commercials than anywhere else in 2012, more than anywhere else in the history of presidential campaigns: 73,000 TV ads, according to The New York Times. In an election with only a handful of states that are considered up for grabs, the importance of Nevada's six electoral votes was highlighted when President Barack Obama chose Lake Las Vegas, a golf resort east of here, as the place to spend three days preparing for the first presidential debate.