I guess he was saying that adding weight in the back end won't make much difference as it would end up being in front of the rear wheels, thus the weight would be distributed to both the front end and the rear end.
Mostrear wheel drive cars (or trucks), it helps if you put weight behind or over the rear wheels for traction. On a Smart, you can't do that because the rear axle is about even with the rear hatch door.
Just a guess..... I like cheese too...