I agree with what somebody else said earlier about Marowak dying, why is that the only Pokemon we've ever heard about that died? it was a little creepy for me...
Other Pokemon probably have regular animal deaths. For example, you wouldn't mourn the death of a fish that brought you the fish stick that's on your plate, but you'd mourn the death of your dog.
Likewise, you wouldn't mourn the death of the Magikarp sticks on your plate, but you would mourn the death of your Growlithe.