I think the point is that the giraffe is REALLY thick skinned. In fact, some argue that as a game animal it is best grouped with pachyderms (but giraffe are ruminants).... Also that the position of the organs is a bit unusual. I agree, a giraffe with a big hole it the heart should not go far, but you need to put the hole there and the bullet needs to get there.
Here is an idea of what I'm getting at regarding shot placement:
http://www.africahunting.com/hunting-forum/firearm-shot-placement/222-giraffe-shot-placement.html . There is a real risk to shoot them in the guts. Look at the back of the front leg relative to the heart and lungs and see how far forward the heart is. Apparently a lung shot can lead to a long follow up. I would use the point ("<") shape of the shoulder joint as a reference point.
Add to that that you are standing below the target in most situations and that the shot position is likely to be at a slight angle and not perfectly broadside. Visualising the organs in the chest cavity - what you are actually shooting at - will be harder than normal, but the range will potentially be shorter.
By the way, from what I've seen on the net the heart pumps 16 gallons a minute.
Never hunted one, but being South African I've read and researched and chatted a lot about our local game animals and I've seen most pretty close up.
Sverre, you will enjoy this I think...