I don't think anyone could develop PTSD simply from viewing disturbing material - after all, part of the criteria for diagnosing PTSD is that the patient has experienced something traumatic that involved actual or threatened serious injury or death. I think it has more to do with experiencing sheer terror and helplessness than just being grossed out or disturbed.

It's an interesting thing to think about, though. With the way the internet is booming and now synonymous with our day to day lives, it will be fascinating to see how that effects the development of psychology in the future.