Also, their schedules to and from OAK seem a little odd to me. In each direction, there are two flights 50 minutes apart, then a three hour wait, then two more flights 50 minutes apart, then another three hour wait and so on throughout the day. It seems like they would want to spread their departures more evenly throughout the day, such as a departure every hour and a half to two hours.
Southwest may come up with $39.00 fares all the time, BUT, in order to qualify for them you have to make your reservations 2 weeks in advance AND (this is the important part) you have to stay overnight. Not neccessarily a Saturday night, but overnight nonetheless.
On jetBlue's website they state that all their fares are one-way and a Saturday night stay is never required. However, if all their fares are one-way, it would stand to reason that NO overnight stay (Saturday or any other night for that matter) is required.
Let's suppose a business person finds out 2-3 weeks in advance that he/she will need to attend a one-day seminar in OAK, flying there and back on the same day. On jetBlue their round trip fare would be $108.00 plus PFC and security fees. If booked online the fare would only be $98.00 plus fees.
On Southwest, since there would be no overnight stay involved, the best one could do would be to buy two advance purchase one-way tickets at $71.00 each way or $142.00 round trip plus fees. In this instance, jetBlue's $98.00 fare represents a 31% savings over Southwest's $142.00 fare.
I'm sure that lots of folks make same-day round trips intra-California, but the question is, how many of them have more than 14 days advance notice? Businesses are starting to plan ahead to save money, so it there are a lot of people reserving 14 days in advance for same day trips, then Southwest might have to consider dropping their overnight stay requirements for same-day round trips booked in advance, at least in markets where they compete with jetBlue.
Personally, I have never understood the overnight stay requirement to begin with. The airline should only be concerned with two things. Are you booking in advance? Are you flying with us both ways? If so, it should be none of their business how long you stay.