It makes sense for them to advertise their website in this way, since the URL is not intuitive. How many people have typed in what they assumed to be the Frontier Airlines website and instead end up with an unrelated communications company?

Not all airlines have the foresight to grab the most intuitive URL for their name (American, for instance, is in the same boat as Frontier). But most have (United, Delta, Southwest, Spirit, US Airways, Allegiant, etc.)