it's the same anywhere in the first world, especially in the u.s., where broadcast media will jump on any early opportunity to make announcements first....to gain viewership. they rely on early sampling of actual vote counts to predict the outcome. for example, when brown was leading 2 to 1 for the state governor race in the last gubernatorial election early in the morning with only 3% of precincts returning, all news outlet predicted him winning at least 60%. for very close races, such as 51 to 49, it's often too early to call until 80% precincts have reported. final tallies in u.s. elections are typically not completed until months later with all provisional and absentee ballots fully counted. life and governance have to move on, and candidates need to concede asap based on statistical sampling and testicular fortitude.
