I left Reddit because both my upvotes and my downvotes were not counted. It took me months to figure that out and luckily I did. I did not care much about the voting system in the beginning but I was lacking a feature that people had and that feature was the upvote notification that lets the person I am interacting with know that I appreciate his/her/their presence even if we disagree.
yes, they do those experiments and they also let other companies do that. I think this is one of the reasons why they are charging more for their API.