Authors may, if they so choose, be extra nice and put a deathfic warning at the start of their story in order to respect the feelings of those who don't like the genre.
However, it is just that. Their choice. Some authors don't like warnings because it may spoil a surprise ending. Others just plain don't believe in them.
umm, "extra nice", eh? Labrat, I'm sure that you didn't mean this to sound as diminishing of both those writers who care about the feelings of their readers as well as those readers who, for all sorts of valid reasons wish to avoid deathfics.
In the interest of balance perhaps you might call those writers who chose not to include a warning as "extra mean"?
I'm not disputing the right of authors to not use a warning. (sorry about that double negative) - I would object to the insertion of "extra mean" as much as to "extra nice.
The difficulty is that the issue involves two competing values - thoughtfulness for one's readers as opposed to the individual need to express oneself. It's a choice made by the author as you say.
My personal reaction? I'm a DJ fan and so I was pleased to see a vignette, feeling comfortable with how she approaches things. (I know that wording is vague

) I trust her. So I was surprised at the ending, although if I had remembered "Bad Brain" I wouldn't have been.

That was a huge clue. So in this case for me (one of those wimpy readers with delicate sensibilities

), no need for that warning.
Ann has been up front with an apology and DJ has graciously accepted it as well as explained what she was doing. Issue resolved.
Anyway ...
c. (who is now wondering about Bubbles aka Babbles

)