I don't think it's so much funny as it is shocking. I had never seen that video of the skateboarding kid and I wasn't laughing, I was gasping at how painful it looked. Of course, people do laugh at such things, and it doesn't make them bad people. We all react differently to a shocking, unusual situation. For some, it's to laugh. This is why slapstick is still consistently popular decades after it was made common on old comedy shows.
I don't think it's in bad taste to show these, as long as the sentiment isn't "guy got what he deserved". It's just human interest to see such shocking things.