This may be totally (sp?) wrong, and, perhaps, ridiculous (sp),
but I suspect it may be due to an old custom. e.g.:
"Dancing was born in a noble and elegant attitude. When a man escorts the lady to the floor for a dance, she should be on his right side. Not only is this the "place of honor", but there is also the symbolism going back many centuries, which implies that the man is offering his fighting arm in service to his lady, and by placing a hand on his arm she is accepting him as her champion. For everyday modern ballroom etiquette, the woman precedes the man to the floor, no contact is required. Once on the dance floor, the man takes a position and extends his left hand to his partner in invitation (palm vertical, towards her), she takes the last two or three steps towards him and takes his hand and then comes into his arms (Exception: Viennese Waltz. Right hand, half turn, curtsy.) The "lady being on his right because his sword is on his left" is just another urban myth. No officer and/or gentleman would wear his weapons at a ball. The man's job is to show off the lady and let her have fun."
I've heard this rule of etiquette (lady to your right), in various other contexts.