Sooo...it's only sort of programming related, but I figure it's election day, right? Is there a single good reason why they aren't, not necessarily open source in that anyone can contribute, but open source in that anyone could inspect the source?
Voting machines aren't open-source because lobbyists for the "electrical till" industry successfully hoodwinked politicians not qualified to make technology choices into buying their snake-oil. This was accomplished with a mix of anti-FOSS FUD and good ol' fashioned bribery campaign contributions.
Update: I will try to post links here from time to time that show how vendors respond to critical examination. Feel free to add your own. (Pro-OSS–only: "the man" can make his own post!)