A story that is sad must be well written in order to have an impact. That's why something like My Little Dashie or Loss works so well. They are well written and make you feel for characters. You can't expect me to be sad BECAUSE you killed of Fluttershy I have to be sad because the death of Fluttershy was built up or I felt it because the characters did. Since we are working mostly with well known characters people think it doesn't need to be felt, but it does, otherwise the death is just a piece of writing rather than something that makes me love the characters and feel for them more than I already did. If the character doesn't act like Fluttershy it isn't Fluttershy.

Agreed.

If there is going to be a death in a story, there needs to be a reason for it other than just shock value.

The best tragedies occur after the reader has had some time to get to know a character or their relationships with other characters within the story.

The best example I can think of that pulls this off well is an anime series called Clannad and its followup, Clannad: After Story. It begins as slice of life with many comedic elements and gradually changes pace to a more serious and ultimately tragic ending.

It works with movies as well, for example: The Toy Story franchise pulled the ending off relatively well because we felt for the characters. If they had done that in the first movie, well it would not have been emotionally satisfying at all. That may be an example of Slice Of Life or So Happy Its Sad but it still gat a similar emotional reaction because we care about the characters. This tactic is important in ANY type of writing, be it romantic or horror. We feel more when we get to know the characters before something important, good or bad happens to them.

Absolutely.

Horror these days tends to fall into the trap of making disposable characters and then setting some kind of killer/monster/virus loose upon them where you almost find yourself cheering on the villain.

Nobody cares about the victims in those kinds of stories.

Exactly.
People try and kill characters off -- disposable or not -- and expect the reader to cry. sometimes, even a sad death will not cut it. an Epic Hero's death will, more often then not, seem like it was epic, but sad... If the hero dies slowly, either alone or surrounded by helpless friends, that is when they cry. Sometimes, though, sadness is'nt everything. Some writers kill characters without deeper story meaning. This is a foolish mistake, and kind of annoying. Do not do this, unless the character was disposable (and do NOT make too many disposable characters, if any).