Catholic Online reports" Bishops Call for Unprecedented, Massive Catholic Opposition to Abortion in Current Health Care Reform"

1. the national conference has a lot of prestige, and any bishop who doesn't want to be branded as a maverick (and few of them do) will feel pressure to act in solidarity with the conference on such a momentous matter; this would be especially true due to the rather unprecedented nature of the action the conference is undertaking.

2. the email specifically addresses the possibility that some bishops may "opt out" and tells the local pro-life people: "If your Arch/bishop is not in
agreement with disseminating the bulletin insert, you will be hearing from
his office immediately. You may wish to check with his office ASAP to see how you may be of assistance in distributing the Bulletin Insert, far and wide."  IOW, if your bishop isn't on board with this, we will help you work around him.  That means that they are serious about this.

Also, while it's true that this doesn't signify opposition to national health
care per se, it's nevetheless true that, to the extent that Catholics heed
the bishops and oppose inclusion of abortion, as a matter of practical
politics it will make passage of any so-called reform that much more
difficult.  The bishops know this, and so do the Dems.