I don't think there should be any difference between service charge and tip. You are tipping for the quality of service you are receiving. One restaurant said the service was to pay for all the incidentals (dishes etc.), which to me are the restaurants responsibility of running a business.
We always tipped too much, until we learned and spent a lot of time in Italy where tips are pretty much the same as in France.
Yes, it's a small amount compared to the cost of a vacation, but would you pay more for any purchase you make than the amount required?
There is always that time when you really want to give more, but that should be your decision. <img src="http://www.traveltalkonline.com/forums/images/graemlins/handshake.gif" alt="" />