Slander is first of all spoken. So, it's definitely not slander. If anything it would be libel, but libel has to involve a public statement that damages someone's reputation. It doesn't apply to a private correspondence. Who the hell was Valve defaming the developer to. Themselves?
The developer is the one that publicized the comments. If they truly thought the comments would be damaging to their reputation, then they would have... you know, not publicized them.
Not to mention the statement would have to be proven false. And Valve's opinion is certainly reasonable.
Not sure if you remember the cases of private conversations in USA that were taped and aired and still got the speakers to face judicial issues.
Prove that Valve statement is false? How and why would the dev prove it wasn't someone from Valve that made? And no, it isn't reasonable, unless you are in any position to claim this game is massively or marjorily consumed by pedophiles.
No, I don't remember a case where someone was accused of libel for statements that they made in private which the defendant then chose to publicize. Because libel is by definition defaming in a public forum. If the defendant chose to publicize those statements, that would negate any libel charges because if the defendant thought the statements would be injurious to their business, they wouldn't publicize them
. Please show me some instance of anything like that happening. Something specifically related to slander or libel, where the defendant chose to release the statements in question.