I believe in USian football, the length of a field goal is measured from the line of scrimmage to the goal line. The goalpost is actually set back in the end zone, and the ball is typically kicked from ~5 yards back.

So wouldn't a "46 yard field goal" actually cover more like 56 yards? That would make the 70 yard rugby kick ~= a 60 yard US field goal. Still impressive - there have only been 20 that long in the NFL.