Interesting study.

It appears that they counted partner reward space as long as it could be searched online, so that means airlines that do not have partner searches online would tend to have more dates available than these figures indicate. Without a lot more information it's very hard to tell how important that would be in the figures.

I don't understand how they searched the same dates for WN. According the WN forum wiki here, the WN schedule ran through August 13, 2010, until it was extended to October 30 on March 23, which is well after the period they said they did their searches. If they waited until the day the schedule opened it would bias the availability upward, potentially a lot.

Highly interesting that only two USA airlines stand out at the low end: US and DL. And by a huge margin.