It sounds like other ticket brokers (Orbitz/Travelocity, etc) still have tickets to sell in the cheaper fare buckets, while US itself has run out of inventory in those fare classes and thus only selling the next-higher fares on its website.

Whether to buy now or wait is a tough call; I guess the standard should be, "If you have to buy now, does it sound like a fair price?" If you wait, you win if the fare goes down later, but would ya kick yourself if the fares spiked?

Sure, it's fine to book Orbitz/Travelocity/Expedia as they are major online travel centers; I've booked through them and everything works as it should, including being in the queue for auto US upgrades ^