From this page:
http://en.wikipedia.org/wiki/Seizure_trigger
"In some epileptics, flickering or flashing lights, such as strobe lights, can be responsible for the onset of a tonic clonic, absence, or myoclonic seizure[14]. This condition is known as photosensitive epilepsy, and in some cases, the seizures can be triggered by activities that are harmless to others, such as watching television or playing video games, or by driving or riding during daylight along a road with spaced trees, thereby simulating the "flashing light" effect. Some people can suffer a seizure as a result of blinking one's own eyes[15].
Contrary to popular belief, this form of epilepsy is relatively uncommon, accounting for just 3% of all cases[16]. In all other epileptics, such lights are no more capable of triggering a seizure than in a non-epileptic person."
So that ridiculous small amount of people that is photosensitive, probably doesn't even play videogames. There are a lot of possible triggers, and if someone didn't have seizures due to flashing lights in earlier stages in life, the risk they will get it now is incredibly small.
And that fear of being sued is stupid as well. Ever heard of anyone filing a lawsuit against a disco?