I agree with Charlie on this one. I speak from experience too. HomeGrown what you are talking about, "lug centering" is called lug centeric. What Charlie is talking about, "hub centering" is called hub centeric. I do believe almost all stock cars/wheels us the hubcentric centering method. But they do make platic rings that fit into hubs that are to large for the hub. This sizes the hole down so the wheel will center on the hug like a stock wheel. It is the best and easiest to get good results. You can tell when wheel is a little out of balance especially with todays larger rim sizes.
Last summer I got my first set of 18" rims for my wifes '99 camry. They sent me the wrong hub centric adaptors. So I ran the wheels without the for week until I got them. You could feel a very slight vibration. Once I put the hub centering rings on very thing was good, no more vibration. On the other hand I had a '88 celica in high school. I put aftermarket 15" rims on. I never had the hub centering rings, just used the lugs to center. It seemed to work fine. But I had to be careful as I tightened the lugs as the wheel would move a little as each lug was tightend.
I'm sure the 15" rims didn't make as big of a difference as the 18". Because the 18" rims have more mass, and more rotational mass, which is also further toward the outer edge of the wheel, i.e. less tire sidewall, more metal rim.
My 2 cents, correct me if I'm wrong, hope this helps
