hsrob on 22 November 2013
The very simple difference is that most of those tackles in rugby were straight up legal so lying on the ground isn't going to achieve anything other than ensure your team is one man down in the line.
If you can convince the ref in soccer that illegal contact has been made i.e. pretty much anything that's not body on body, then there is potentially very large benefit to your team, particularly if you are within shooting distance. The game can literally turn on a single tackle. Don't get me wrong, I think anyone caught diving should be sent off, but I understand the histrionics with any potentially illegal contact.
edit: some of those are pretty funny :)
