The problem with his argument is that he's applying it to one specific issue (abortion). You are correct that he is being completely consistent within the context of the issue. However he is not being consistent at all within the context of the larger argument he is using to defend his stance on the issue.
For example, could this same letter have been written to those that voted for the Pro-War candidate, John McCain? I would argue that it could have. So is he advocating that his parishioners options were either vote for McCain or not vote at all? If so, then he is seriously out of bounds (monkeying with the separation between church and state), not to mention a hypocrite.
Whether I should be surprised by his stance or not is not the issue. The issue is whether or not his actions were appropriate.
Thanks, as always, for your post sir.