"why do you want to get an ad for Southwest Airlines"

From what the example shows it's not so much an ad as a really quick way to visually see that when you click you will be going to the right place.[1]

I mean visually it's probably quicker to see the big honking ad and airplane and focus and click than it is to read type. I'm guessing. User testing would prove or disprove this. (After all why do people use icons for that matter?)

[1] If it looks like a duck and quacks like a duck, it's a duck.