Your post confused the shit out of me. You wrote "up until the polls close", and I was thinking they were going to show live voter tallies as people voted- which would be insane. They're going to show the official results AFTER the polls close. They're getting a direct feed from the state computer systems, the same way they get flight status updates directly from airlines.
Keep in mind that the polls might not actually close until hours after they're scheduled to. Due to Republican sponsored voter suppression, the lines to vote, particularly in Ohio, could be several hours long.
http://fortune.com/2016/11/07/google-election-results/