What? That they bought the game or that reviewers are given free copies to evaluate?
It's a commonly accepted practice in entertainment media to get free access to the thing you're going to report on. Dinner, drinks, hotel suites, gift bags...these are the things that sort of or definitely cross the ethical line. A single free copy of the game for the purposes of evaluation isn't an ethical breach though. And if it was...it'd be between a $5 and $50 breach of ethics
Stuff like that is only unethical if it influences how you report/review the game. I don't think a single free copy earns any dev houses any special treatment. Unless the reviewers are complete amateurs and are grateful for even being noticed.