Why our game never appeared in the new section of the appstore? We released a game 4 days ago (Thursday), Junction Action Arcade, its categories are action and arcade,
and I've been looking in the appstore in the section "Games -> Action -> New", in tha USA store, and it never appeared there.

Doesn't every new release appear in that section sometime? Or how does that work?
You actually want to look in featured games->action->paid which allows you to sort everything by release date or name. 

The "new" category is horribly broken or useless for some reason and only seems to contain what apple wants to be there. Also the "new" apps section contains a lot of items that aren't even new! Changes are in order with ios7. 

Unfortunately this isn't going to be clear to your actual potential users.