RustyC

If you factor in the bags (and infrequently flying families aka Kettles tend to need some and can be over-packers), the equation shifts for a number of people, especially around this time of year. Also the free soda and not having to worry your family will be split up to middle seats for not paying the seat fee (even though you don't get an advance assignment on WN, you have a better chance of sitting together with their boarding groups, though it may be across an aisle or something like that).

The 2 bags + carry-on is the biggie, though, and WN is betting people will figure out that if they need the bags they'll be as well off with WN. It's a bet on the intelligence of consumers and that can be risky, and there's a lot of Wall Street pressure for WN to charge for bags. I've seen two cases of entire families of 4 trying to go with only carry-ons on a legacy (one had a matching set!) but with Spirit and Frontier they charge even for the normal-size carry-ons, and at a higher rate than checked bags. I doubt I'd recommend the ULCCs over WN if an infrequent flyer asked me which to pick to take a family to, say, Orlando for a week.

Airline baggage fees, BTW, have been an unsung story in terms of being enormously damaging economically. It's one of those Freakanomics things and I don't have the statistical tools to prove, but the charges and limitations are a great way to crimp what people buy on vacation. Much of it is frivolous (moai-shaped liqueur bottles?) but is economic activity nonetheless and income to someone. By looking out for numero uno, I'd bet airlines have created many times the extra generated revenue for themselves in foregone purchases because of people being forced to pack lighter. But that's a whole 'nother discussion.