Why no appreciation of the apology? If all people are going to do is find fault with people apologizing, why bother? How should Tumblr reacted? What are they supposed to do?
Perceivedly, it happens a lot that big scary companies bully smaller entities with meritless but expensive-to-fight legal threats. That sometimes there's enough of a public notice of that to make the company reconsider and to limit the damage done is just part of the game and doesn't really leave them without blame, it just means they got "caught" this time.
Instead of bashing Tumblr for apologizing, we should be happy they retracted. If HN was the reason why they retracted, then great. But let's stop looking down on Tumblr purring ourselves at the top.
We are all at the same boat and same level. We are all trying to make our companies work.
The thing to note in all this is:
"Our legal department very recently started using a third party vendor to assist us in pursuing trademark infringers and, due to an error in our new process, your domain was mistakenly caught in the cross-fire."
If tumblr has switched to yahoo! legal, that is not a nice side effect of the acquisition.
Of course it's not for me to accept or not accept that apology and no one should care about my opinion on the matter. But I think not appreciating the apology is a defensible position to take and I'm trying to articulate why I feel so. Feel free to dismiss me. :)