I think a lot of it has to do with the size of the community. On a smaller site you're more accountable for your ations as people will remember you. But on Youtube it's a different story. That site is so big that you feel completely anonymous and thus can say whatever you want. There aren't enough mods on the whole internet to keep Youtube in check.
"Now, a fun game should always be easy to understand - you should be able to take one look at it and know what you have to do straight away. It should be so well constructed that you can tell at a glance what your goal is and, even if you don’t succeed, you’ll blame yourself rather than the game. Moreover, the people standing around watching the game have also got to be able to enjoy it." - Shiggy
