Showing any infinite-sized object in 100% form physically like that is simply put, impossible. By that logic GOW would have to show the Underworld having no limits within the game itself by physically showing it without any statements, despite the bonus video within GOW1 itself involving the main concept artist, the GOW1 Bonus disc, the Prima Guide which repeats the same exact shit as the Bonus video, Temple of Helios and one more WoG (Cory himself, who confirmed the Bonus Video's statement to be true) stating otherwise. And here's the thing: None of the size statements are ever contradicted in any measure by the games, ever. Especially with regards to the Greek Underworld.