Um sorry, I think you are misunderstanding my post. I never said that all tents needed to be staked down - In fact I said in my post that "a freestanding tent is any shelter which doesn't require stakes or guylines." And no, I do not carry my "tent down the trail already to sleep in." Where I camp, it is often heavily wooded and the ground is very densely packed with rocks and stones, which make it a nightmare to find a place to stake down a tent. When I get into camp with a freestanding tent, I can set up the tent wherever I want (preferably a more open area) and then find a spot where the tent can fit and can be staked into the rocky ground. Sure I could just throw the tent somewhere without staking it, but whenever there is a chance of rainy, windy, or otherwise inclement weather (which is basically a given whenever my Boy Scout troop camps) I would definitely want the tent to be fully staked out.
You are right, I failed to mention another purpose of freestanding tents. They enable a user to setup a tent where tradition staking is impossible, such as the slickrock country of the American Southwest. However, there are alternate means of staking such as using rocks and other objects. See this excellent article by Mike Clellend (http://www.backpackinglight.com/cgi-bin/backpackinglight/ditch_your_stakes.html) for more information. So once again, the freestanding tent is not truly necessary.
BTW, maybe I was just being ignorant, but is there any tent with a vestibule that is completely freestanding (meaning it has no vestibule that needs to be staked down). I would be curious to find such a tent. I thought that to be "truly" freestanding it would have to lack a vestibule.
For some more discussion of the definition of freestanding, check out this thread: