Ed Peters reports and updates his original post:
USA Today is now reporting "Vatican spokesman, the Rev. Federico Lombardi, later issued a statement approved by the pope clarifying the [pope’s and his own] remarks. The statement said the pope did not intend to excommunicate anyone. Politicians who vote in favor of abortion should not receive the sacrament of Holy Communion, Lombardi said." Read on, and you’ll also see that the Mexican bishops have not excommunicated anyone, and that what this event boils down to is but the CORRECT application of Canon 915, which is all some of us have been urging for a long, long time.
Am I glad the interpretation I set out below was correct? Sure, what lawyer wouldn’t be? But I am more pleased that a sound and pastorally effective reading of canon law is being promoted. Make no mistake: denial of the Eucharist is grave consequence to seriously sinful behavior; moreover, the pope’s comments leave open the possibility of escalating the canonical response to pro-abortion agitation by Catholic politicians, even to the penal level of excommunication. But we see clearly here that all of this must happen in accord with the requirements of law, the same law that seeks above all, "the salvation of souls" (1983 CIC 1752).
Update: Kudos to John Allen Jr. for providing the whole transcript to the questions the Pope answered aboard the Papal plane. You can now read what the Pope actually said in response to two questions one on abortion and Latin America and another on excommunication. There are also other interesting answers and one dealing with Liberation Theology.