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!)
- Interesting Email from Sequoia
