Good question. But the article isn't about all voting machines, just Diebold's extremely lax security in theirs.
Does anyone use non-rewritable media for electronic voting? If not, some of the same issues are just as applicable to other systems as to Diebold's. To be sure, the succeptibility to outsider cheating may not be as bad on other systems as on Diebold's, but any system with rewritable code will be subject to undetectable insider cheating.
By contrast, putting code and votes on non-rewritable media would mean the only way to cheat would be physical substitution of the media in question. Use of well-designed serialized holographic seals could make such substitution sufficiently difficult as to no longer be the easiest method of fraud.