For the business trips I take on WN, I often don't finalize my itinerary until a day or two before, and my return flight is often changed on the day of departure. As others have pointed out, the apples to apples comparison is comparing the BS fares to Anytime fare. BS tickets gets me a low boarding pass no matter how close to depature I book a flight, and is absolutely worth it.

On personal trips on WN, I usually plan weeks to months in advance, and always take the lowest "Wanna Get Away" Fare