I am also European (
Maltese) and have never experienced Wedding rings (bands in US) worn on the right hand as standard practice. This might be yet another
rumour being spread about those alien beings who do not live in the
US.
Being rather
utilitarian and considering
function, rather than
form to take precedence, I imagine that the left hand is chosen to wear a ring on for practical reasons. Since the majority are right-handed, this hand is left free from
foreign objects that would in some way
impair every-day activities performed with the
dominant hand.
Hark back to the days where wearing a sword was standard practice. The said sword was worn with its hilt above the left hip for maximal sword-drawing efficiency. Anything worn on or around the fingers on the right hand could only
hamper this at best and cause injury at worst.
Another, slightly less
mundane, reason could be the ease with which one can keep his or her left hand hidden inside a pocket for the entire duration of a conversation with an
attractive person while in the absence of one's spouse.