The ones which do use the rudder are usually listed as limits and the ones without are demonstrated.
Guys, whatever you do, be careful whatever you do. It's not a testicle-size competition.
There seems to be many theories on this. As
Sgroogee says, it just happens to be the strongest crosswind demonstrated to the authority during the certification phase. If the wind didn't blow then it is low, if it is then it maybe the limit of the aircraft, but you don't know that. Therefore, I don't believe the demonstrated limit actually tells you much at all about the true limit of the aeroplane. My experience is that I am more than capable of landing in excess of the demo limit on some aircraft and am not really upto it on others. That isn't a recipe for gonad growth, simply an understanding of what the numbers mean.
FYI
http://www.gulfstream.com/product_su...GIV_OIS_09.pdf
http://www.gulfstream.com/product_su.../GV_OIS_01.pdf