I'm left wondering why they brought a guy who calls himself a "child" psychologist on to discuss the bystander effect. Truly they could have gotten somebody who does their work in violent behavior?
Either way, I think that movies & TV would have a larger effect on "violence desensitization" (if such a thing exists) than videogames would.
Everyone I know who was made aware of this event was made sick by it (in some form or another). Truly, if there was a "violence desensitization" effect, less people would care and this wouldn't be made national news.
Ironically, the fact that this psychologist's opinion was briefly made national news is evidence against his theory. I.E., if people were desensitized to violence, the event wouldn't be as noteworthy as it is, and therefore wouldn't have been broadcast.