I agree that being paid a living wage is better than being paid too little to live on, but some jobs are simply not worth what the government sets minimum wage at. Besides, it is not the large companies that lose out because of the minimum wage; as you pointed out, they can afford it. The people who lose out are small businesses, who do not have the massive amounts of revenue that large companies have.
If Wal-Mart could start paying employees less, it would only cause itself to lose money in the long run, as employees leave for better jobs at Wal-Mart's competitors. Wal-Mart has an invested interest in paying its employees properly. You even state that they pay them above minimum wage...that doesn't seem like a company who are actively trying to pay employees the absolute minimum.
If Wal-Mart could start paying employees less, it would only cause itself to lose money in the long run, as employees leave for better jobs at Wal-Mart's competitors. Wal-Mart has an invested interest in paying its employees properly. You even state that they pay them above minimum wage...that doesn't seem like a company who are actively trying to pay employees the absolute minimum.