Quote Originally Posted by Captain Fishpants
Endless blood and guts don't add anything much except an icky factor that only the slightly warped will really enjoy. And rendering out pixellated guts uses graphics processor resources.

The violence inherent in a game is only part of the rating. There is also the bad (or otherwise) language to consider and the general content of the game. The PEGI system used in Europe manages to rate games by age, and draws attention to any special areas of concern such as profane language (the generals' speeches alone helped M2TW to a higher rating for that!), sexual content (if any) and the like. Check out their website for more information.

The US ESRB system is slightly different, and can result in a different rating. Generally speaking, violence is of more concern in Europe, while "naughty" language and sex pushes up a US rating.
Bearing in mind we had some of the nastiest wars here... and the german game laws caused TS (Tiberian Sun) to have its corpses look like those silly little andriods