I totally agree with you, it was a little heartbreaking because they all knew it wouldn't be fair to put the blame on someone... It was a very bittersweet post, but it was a wonderful portrait of Severus' evolution as a character. In the early SnB days he probably would have hexed Serenus into oblivion!
I wanted to hug Severus too, but I don't think he (or his mate) would appreciate that very much :P