The island wasn't really purgatory though, all of that was real, it was the most important time of their lives. The "alternate reality" we've been watching this season was sort of a purgatory. They've been saying on the podcast all along that those were not "alternate" to what was going on on the island, and that they must be events occurring at another time. The great twist was in that other time being in a place where time didn't matter.
I loved Ben hanging back, I assume because he had good to do with Alex and Danielle and the kids he teaches. I really like purgatory Ben, it was good to see him happy.
BTW, did anybody else catch the Target commercials during the show? The smoke detector one was great. If you were watching on DVR and fast forwarding commercials they would have been easy to miss.