I do think that they believe getting back on defense is more important than going after an offensive rebound, but I also don't think it is planned that way.
I think they are working with the players they have. If they had a quality offensive rebounder, they would set them loose. However, they simply don't have one on the roster, and haven't really since Leon Powe left. So, they work with what they have, and try to emphasize their strengths.
If they can be great defensively, and incredibly efficient offensively, then they can basically hide their weakness on the boards.