I have an 2006 XB12SS and couldn't find one either. I know there isn't one there as I have the whole front end apart and the trees/modules/fork uppers sent out to powder..
However, I did notice another ground point on the RH frame rail next to the battery (across from the normal ground point on the LH frame rail, where the neg battery terminal connects to. I don't remember seeing this on my XB12S or XB9SX, so my guess is that the SS grounds there instead of the triple.
I believe the ground points are dif between the r and s models. The ground point by the triple is for the r.