User blog comment:UFO Editor/Season 7 spoiler thread/@comment-3411410-20110308065410/@comment-392210-20110308110521

They didn't explain it... he just stopped appearing. He stopped appearing even when Shawn Pyfrom was still a series regular (although out of the last 12 episodes of season 5 he was in only 3).

I don't like it when other people narrate. The show is supposed to be told from Mary Aliced's p.o.v., other people doing it kinda ruins the prospect of the series. Not to mention that no one is as good as our beloved Brenda Strong.

However, I hadn't though of that, and it's an interesting theory to take into consideration. A different narrator was shown in seasons 3 and 5, two years appart. Maybe now, two years later, another deceased character narrates.