The Giants were 2 points down, but in a position they were almost guaranteed to score at least 3 points with a kick.
Tom Brady is a great QB with a great offence and 7 times out of ten could get the points back given a minute on the clock.
What the Giants really wanted to do was score with no time for the Patriots left to score back. The Patriots Defence probably intentionally went soft on the play, allowing them to score, so Tom had time to drive down and score himself, leaving no time on the clock.
What the guy scoring should really have done is dropped to his knee on the 1 yard line allowing the Giants to finish the game with the final score as time expires.
It is risky though, ask the Ravens who in the Semi Final missed a 'sure thing' kick and missed out.