In regards to the changes in availability in each fare class, my experience with US Air is that they have rolling fare class inventories. In other words, they don't initially make available for sale all of the inventory in a particular fare class. They will make a certain number of W class fares available. When those are sold they may let a few weeks go by where tickets are only available in the remaining (higher) class fares. Then they may load more W class inventory at a later date. My guess is that seats are not selling on those routes so rather than have a fare sale, they will merely make more seats available at the previously unavailable lower fare.