This is actually a well known phenomenon (http://en.wikipedia.org/wiki/Bystander_effect). It's why, in a crisis, you should always single people out to do tasks instead of saying "someone do this". Otherwise everyone will just assume that someone else will do it.

No. An entertaining was doing something people assumed was part of his act. Their are also conflicting reports, both here and in the actual comments of the article.

Suffice it to say, it's still too early to know what was going on. But it wasn't just some guy having a stroke and no one doing anything.