I see in the video that we find a pip boy and put it on, so that got me to thinking what would happen if we just walked past it? I'm guessing that it's either a scripted event or that we need to wear it to get out of the vault.

Also I haven't watched all the interviews yet, did they mention if we would be able to enter every building we see, or will it be more like FO3 where half buildings where just scenic and had no interior?

I would think the Pip-Boy find will be a scripted event. Not sure about the buildings other than some will be destructible to some degree.

The Pipboy seems to be on the elevator you go on to enter/leave so I'm guessing you pick it up as you leave the Vault (probably scripted)

No sure about the entering every building But I'm guessing since you take buildings apart and rebuild them I guess a lot more will be useable.

It's most likely just a scripted event, I doubt they would let you leave with the thing that lets you do more or less everything when it comes to viewing and sorting your character and items, though it would be an interesting playthrough going into the wasteland without one. As for the buildings, I feel like they will definitely have way more houses you can go into than FO3 but will still have a couple that are boarded up/INACCESSIBLE.

it's totally possible to have the player take it without it being a scripted event

(like you need one as a remote opening device for a busted vault door to even get out or whatever)

http://www.nexusmods.com/fallout3/mods/5573/?