In a sense, it doesn't matter whether the curious "american inventors" search results set comes out of political bias or technical inadequacy: from the perspective of many people, Google's editorial choices in certain areas have forfeited the benefit of the doubt in others.

This situation is a good example of why it's important to pay attention to maintaining the appearance of impartiality as well as actually being impartial.

(Disclaimer: I work for Google. Nothing related to search.)