The price per
cm3 is just a easy way the present the total costs to the custumer. This price includes obviously the cost of the raw material but also the average cost of the machines plus the average cost of the man power needed plus the average cost of shipping divided by one cm3.
It is quite usual. For instance, in my company, we charge by
man.month rate. But this man.month rate is not the price we pay our guys (our own raw material
). It includes the taxes, the fix costs like the monthly cost of the computers, the monthly cost of the buildings rent etc. and this for everybody in the company (including those not working on things we actually sell, like administrative people) divided by the number of people actually working on things we sell, and this give us our month.man rate. Then we multiply by the actual number of man and the number of months actually needed to perfomer a task to charge our custumers.
For the same reason the price of a cloth is not only the price of the fabric...
But as Glen said, there are plenty of (smaller) things you can do with 3D printing to personalize your motorcycle.
In my view, personalization/customization is key since generally you only build one copy of your object.
Enjoy 3D printing!