Yes, the business model works for those who don't mind making a connecting flight for nearly every destination, no first class/upgradeable cabin, and have no desire to fly internationally.

You can put WN up against FL and you'll have a clear winner. But the legacies are different animals catering to a different kind of traveler. Comparing WN to DL is like apples-to-oranges, or at least grapefruits-to-oranges. They overlap in only a small area: domestic-only travelers who don't want to upgrade to first class.

This certainly does have financial and marketing advantages for WN, and in my mind makes it easier for them to drive a profit.

But it's not like WN is rolling in fists of cash, either. Their meager profit is still nothing to write home about. The whole airline industry is in trouble, and much of the reason why is because people keep demanding $49 flights and revolt when an airline tries to charge a baggage fee or a ticketing fee to recoup some of the losses from those rock bottom fares.