Yep, they stopped calling it road tax and called it "vehicle excise duty", basically because the amount you paid didn't relate to the amount spent on the roads any more, in other words, it was a tax not a "price of using the roads" and some of the money goes to other government spending like welfare, Trident missiles, MPs expenses, etc etc.
Except that if you don't have a car, you don't need to pay it. Or, you can have a car, but if you don't go on public roads, you don't need to pay it either.
Going on the original poster's theory, does that mean thos who get classic car tax (pre 72 or whatever) should be treated like cattle, on the roads?