It's the so-called Puffing Rule. Puffery, as it's called, is said to be statements which are unlikely to mislead or deceive consumers - usually because people are not expected to believe the claim as a statement of fact. When writing about puffing, courts acknowledge that people expect advertisers to make claims regarding the general superiority of products. Judges believe consumers will not rely upon these claims when making a purchasing decision. Unfortunately, there are no clear guidelines.
Courts even make inconsistent decisions.
One court decided that a company was merely puffing by claiming its lamp is brighter than others. However, another court decided that an ad claiming a snow blower to be easier to push and simpler to maneuver was unlawful deceptive advertising. Well, that's really not the way most businesses do business. Especially if it's the business of running the country. Or advertising to be elected to run the country's business.