You are misinterpreting your link. GDP only includes economic activity, not assets such as inventories. Your link clearly shows that GDP includes CHANGES IN inventory. If businesses push more inventory out the door than it receives, that is an increase in GDP, and a sales tax will capture it.
A flat income tax does not tax inventories or business investment either. That's why I said a sales tax and a flat income tax are economically equivalent.
Correct. Actually I was misinterpreting your post.
Actually that is arguable. In most analyses I have seen the sales tax would create a boom economically. Jorgensen put the GDP spike at upwards of 10%. The "tax haven" effect is enormous as well. Jobs, jobs jobs.
The flat tax would be simulitive also, assuming the rate is low enough, but nowhere near the amount the fair tax would be.