its not a coincidence, the three (military) satellites are actually moving in a triangle formation to more accuratly calculate the position of objects such as ships. several of these 'tri-satellites' (not really called that, but sounds good
) are in orbit, launched in the late 80's and early 90's by the US. The US actually denied there existance until the early 90's.
late 2006 I observed one formation for about a week. each night the satellites would appear about 50minutes earlier until it was too early in the evening to see them due to twilight.
Jarrod.