Peter,
If US states are using homegrown systems, and they probably are, that doesn't really have any impact on my thesis. One's nationality doesn't oblige the person to defend the methods of his government.
All I would say is that economies of scale are critical in high quality systems. Some systems, like ICBM guidance systems, would probably be made better if the US and Russia cooperated on them. Nonetheless, sharing military data between potential adversaries is typically worse strategically than any gain at a system quality level.
As for voting systems, if they are made and implemented in a trustworthy way, there benefits from scale that outweigh security or economic concerns. First, it seems self-evident that typical saboteurs would be domestic in any given election. Even if there were foreign actors, they would need domestic support who would presumably have better access to domestically built software anyway. Sunlight is the best cure for that problem - not domestic development.
Second, voting is a very common occurrence in the world. Kenyan companies have an actual opportunity to develop a robust and exportable voting product. Kenya is sadly world famous for voting problems so if in the next 2 elections, it could demonstrate a platform that is robust and durable, it could be made into an actual product that other governments might buy (or if open source, contribute to). This would be a fantastic challenge for the local ICT industry and potentially a huge boon. However, institutionalizing the case that all voting systems should be homegrown would kill that company's export reputation though.
Finally, if Kenyan ICT 'national pride' rests on developing its own voting platforms solely for Kenyan elections, that's a major problem. Everybody's got to think bigger - people like me want Nairobi to be a capital of tech in Africa and the world and the only way to make that happen is to give the entire industry an international focus.
-Adam