Okay, here's why this is wrong
"WARNING: Exposure to violent video games has been linked to aggressive behavior."
The thing is, the link itself may be SO insignificant that it could be a mere 0.1% link, opposed to something such as "WARNING: Smoking is linked to lung and mouth cancer", where the link is proven to be much stronger.
Your average person is in no way affected by exposure to violent media, interactive or not. The rare exception that results in tragedies cannot be blamed on the trigger in a person who was susceptible to violent media in of themselves.
The wording is also so vague that "aggressive behaviour" come range from a school shooting to a murder, to a misbehaving child throwing a temper tantrum.
What's more is that if these studies that show the link are government funded, we run the risk that these scientific results are biased to produce desirable data for a cause, instead of actually retrieving the truth. It has happened many times before for personal profit.
How far are they willing to take these warnings however, will they start forcing gruesome images of the negative consequences of
smoking playing video games, too?
One last thing to consider. This will have zero impact on the online distribution of software, it at best will only ugly up the boxes on store shelves that'll discourage parents from buying these for their underaged children. Rightfully they should, but they'll be doing it on misconceptions.