Arquette/Harper-- Weird Coincidence

10/11/2010 7:07 PM PDT
Best friends do everything together ... and in the case of the Arquettes and the Harpers -- they even call off their marriages around the same time.

Back before the two power couples each called it quits -- the foursome spent a whole lotta time together throughout the years ... because Laura, Ben, Courteney and David were all best friends.

So David and Courteney separate several months back -- and suddenly Ben pulls the plug on his marriage.  Coincidence?