Tragedy is a commonly misunderstood and misused concept. True tragedy does not occur when a plane crashes into the maternity ward of a hospital and kills hundreds of babies and pregnant women - in fact, babies are pretty much immune to tragedy (more on that in a moment). Nor is it tragic when little animals are orphaned or when Princess Di intersects with a concrete pylon at high speed or even when lightning strikes you on a clear day.
Real tragedy is based upon the notion of the fatal flaw. For something to be genuinely tragic a catastrophic and (this is the important part) otherwise avoidable downfall is suffered by someone as a result of a single, critical flaw in themselves that causes everything to come undone. Macbeth is tragic because Macbeth, despite being a rich, pleasant and well-favoured guy, is cursed with the fatal flaw of ambition which lead to his moral and physical destruction. As mentioned above, tragedy incorporates a sense of the inevitable and is often married to the greatest desire of the individual in question (for Macbeth, to be king).
The media must take the bulk of the blame for transforming the idea of the tragic into something meaning 'really really really BAD.' Newsroom favourites such as bad things happening to babies and cute little animals and people being struck by unexpected and bizarre accidents are in fact the absolute antithesis of tragedy because the victims are innocent and their death or maiming is the result of the random vicissitudes of life and not some inherent character flaw of their own. Thus the more innocent you are and the more arbitrary the nasty thing that happens to you the less tragic it becomes. Sadly, like many other useful and interesting words tragedy will eventually be totally absorbed by people looking for dramatic ways to say 'really really really BAD' and it will be left to wizened English Professors and Shakespeare hacks to know the real meaning.