I beg to differ: a friend of mine was violently mugged in Nuku'alofa last year and ended up in the hospital with a concussion. It was the 1st day of his visit, he was on his way back to the hotel and he asked the way from a friendly local... who directed him into an alley where he was promptly clobbered by three masked men.

For what it's worth, according to the police he had the dubious honor of being the first (non-resident) foreigner to be robbed in 2004, so the odds of this happening are rather low. But don't throw all caution to the wind