If you visit the privacy settings of Google Search it specifically states that it will store your search history on its servers and that you can access it and delete it. What Google doesn’t do is separate voice search from keyed-in search. The same rules apply to both.
Google has always saved the history of searched terms to further improve its services, and they’ve been transparent about this from the beginning. From Google’s point of view, voice search is just an extension of the ‘regular’ or text search. And you can readily see the mode of search in your history.
The huge amounts of data that we are creating can be a valuable asset to improve user experience. I would prefer that Google show me Indian restaurants near Washington DC based on my recent searches instead of showing me a random bar in a faraway city.
So before you get all worked up, think about how you use search and whether you want to delete your history or at least anonymize it (you can turn off the voice activity so that even if Google records your search terms they can’t be traced back to you). Google gives users have complete control over the management of their search history. It’s up to you whether you want to take that control.