YES it is absolutely true.
If by everyone you mean everyone on this forum. The other forums with Dom3 populations also tend to play the same, but not the same as this forum. Also the are the various Dom3 IRC channels. Part of the problem isnt just that they play the same but that they tend toward playing the same game all the time. The same game settings and the same size or style of map tends to define what nations and tactics are strong or weak.
There is a thread here about game variations but its rare to see one of them tried.
http://forum.shrapnelgames.com/showthread.php?t=35083