Once again, a case of a perfectly good 6-mile course ruined by trying to force it to be a 10 km. I see this a lot more in the 3 mile/5 km area, but only because the shorter distance is more popular.
Coming from New England, where "odd" distances of 4.78 and 8.4 miles are common, we don't believe there is a "magic" distance - wherever the race starts and finishes, that's what it is.