Holly Marie Combs was still pregnant when this episode was filmed; she gave birth to her son Finley only a few weeks before the episode aired. In the hospital scene right after Chris's birth, a stand in was used to make it appear as though her baby bump had disappeared.
Every season finale thus far has ended with the closing of a door to signify the closing of another chapter in the charmed ones' lives (season 1+2: Prue, season 3: Shax, season 4: the angel of destiny, season 5: Chris). This is the first season finale to use a door other than the front door of the manor. This finale is also unique because the door is not closed by magic.
Gideon says that Wyatt cant orb out of the underworld yet, because he would not be powerfull enough. But in the episode Sence and Scence Ability (s05e20) Wyatt orbs himself and Piper to the underworld to the place where the Crone keeps Leo prisoner.