It looks like we're going to have an interesting debate here! Hooray!
The first thing I've got to say is that everyone has the right to decide what they believe is art, and what is not, me personally, I believe that everything can be considered as art.
So 1, art is personal, and for me, these images are art, the circumstances surrounding them are sad, not ideal and that cat needs a bell. The fact that the images show death don't detract from their artistic value, nor do the grisly circumstances surrounding them. If anything they add an extra artistic element - that of reaction and debate.
Let's look at a few images of my pseudo artistic bollocks, I'll gladly show the world that I'm disgusting, perverted and possibly brain-dead

(trying to put smilies in to show that I'm getting involved in debate and not taking offense at these valid points that have been made!):t:
1) A dead sparrow, just a photo. Art? record shot? Disgusting? Beautifully tragic? Sick? Glorifying death?
2) Same sparrow, but now painted by what is known to normal society as 'an artist'. Does this change any reaction?
3) A pair of Common Terns, beautiful picture - detail, colour, tone, mmmm, quite a popular piece this one, until you look and see that one of the pair is upside down. I could have painted this scene from a few hours earlier, before one half of the pair killed itself by flying into netting on the same tern raft, being rescued, taken to a vet and after not recovering put back for the remaining bird to see that it was alone in this breeding attempt, it abandoned the eggs about half an hour after. But perhaps this is just documenting the scene, it's just a picture of a sad story. ?
4) Dead Barn Owl, found on a road and put on a nature reserve sign, interesting combination of dead bird and protected area. Getting close to distasteful now perhaps?
5) Troubled 15 year olds always manage to find something to do with a dead moorhen, the lyrics are radiohead.
Hope this keeps the debate going, looks really interesting!