The safety early in the NYG/Dallas game.

Romo is hit around the 3 yard line, stumbles backwards, almost regains his balance, but then falls down in the end zone. The safety is called immediately, and no one seems to debate it - coaches, players or announcers.

I don't get it; if he was hit around the 3, and it was that hit that caused him to go down, shouldn't the ball be placed at that spot? If he was ruled to have escaped that hit, doesn't he need to be touched again to be down in the end zone?

Little help, please?