Hey Jack,
I don't know if that does matter in the States but in Germany when the car manufacturer states weight in the car documentation than they calculate like this:
Car with no option + average weight of a driver (68 kg) + 7 Kg add. weight (for tools, etc....) + 90% of a full tank.
In the earlier years (80s, 90s..) they just considered car weight with no options + average weight of the driver + 100% full tank.
that makes is more complicated, right?
Shahram