If they lose or draw a match, yes they would lose more points than they would were they not hosting. (It's why they dropped out of the top 4 last year as well.) But considering that they've won their first two games in this tournament, they haven't been hurt by home field advantage. They haven't been helped by it either, as it's reduced the number of points they've been able to earn, but they've still earned points from those wins (their opponents weren't so far beneath them that they could "not win by enough") so they haven't been noticeably hurt yet either.
Japan vs North Korea live now(ht score, 0-0). If they win, Uncle Kim promised his players a double ration. Kimchee bowl. Let's see the Japanese beat that!
North Korea with a cracker! 1-0 take the 1-0 lead. Japan finally brings in their top player, the #7. 20 ninutes to go
another whole sale destruction of the Nakeshiko at the feet of North Korea, 0-2 thoughts; before the endless sake parties & pachinko games, you Japanese had a 'bushido code of honor'. I recommend you follow that honor by voluntarily give up your top ten ranking to N. Koreans(as those idiots at FIFA have just dropped them). It would be the 'fair' thing to do!