I have been wondering why the warning above is always sounded in many news bulletin. I am aware of a rare medical condition (flash sensitive epilepsy), does the flash contained in many of these short clips great enough to trigger seizures in sufferers of this condition? Or is the warning just some regulatory TV protocol that must be fulfilled? Many thanks for ur response....

No it isn't just a warning for the sake of it. Flash photography, even on a TV screen, can and DOES trigger off a seizures in people that suffer from photosensitive epilepsy... it's actually a very common trigger. And in some sufferers video games and fluorescent lights can also trigger a fit.
When I'm shooting an event I try as much as possible not to use a flash but still make sure they announce that there will be 'flash photography'... just in case.