There is actually a very serious point here, regarding the use of the Internet by terrorist organisations, and I think it shows that the net is a much more powerful medium than any that we've had access to before. I'm not sure if terrorists et al are aware of it, or they're just using it though.
If you watch something on television, you as the viewer don't control it, the tv company does. All that you can do is to choose not to watch something. Another point which is in many ways minor, but I think is also pertinant is that the tv is across the room from you. Consequently there is a distance between the viewer and what they're looking at. It's also contained to a greater extent because the television is in a corner of the room, it's easy to look away from and we've developed the ability to blank it out and talk to friends over it, or get up and leave it to go and make tea.
With the net, it's rather different, and the viewer has much more control. You usually search for the image or video, and you directly control the speed, pause, zoom functions and so on. You can also watch it over again if you wish to. Consequently, the image/video is much more 'real' than something on television, and as a result it has a greater power to shock or upset. Terrorists are therefore able to bring things right into your own home to a much greater extent than they can do with footage released to television companies.
I've not seen either video, nor do I wish to, but I'm not in the slightest bit surprised that they are distressing.