Moore actually had a very good training camp. Some of the beat writers like Greg Bedard posted at times that "he had deflected more passes than any other defensive back on the team." Then he also added the words "by far" after his comment.
He's only allowed 2 completions so far on the year, for a total of 9 yards. He also did a fine job with a nice open field tackle on Sunday, and helped to limit Fitzgerald to 1 catch for 4 yds (in a double team effort).
It's Arrington who hasn't looked too hot so far in the secondary, allowing 7/9 passes thrown his way and a TD, not to mention the poorly played tackle that led to 30+ yds on Sunday. Besides Arrington, Gregory didn't look too great, although I also don't think he looked horrible either. The secondary has looked pretty decent so far this year.
As for the poster's comment who you responded to, he was inferring that Belichick was keeping Dowling healthy, not Moore.
Preseason we saw Moore look just fine in the first game, then not as good in his second game (where he allowed the longer pass to D.Jackson, although he did limit him to 1/3 in his defense). He missed one of games 2 or 3, and then played a lot in the last game where he and the scrubs who don't play for the team anymore allowed some bad plays. I don't think you can just look at preseason though, due to Belichick playing specific players in specific roles, along with a very vanilla defense.