3D printing, powder spreading

In a printer like the ones made by zcorp:

http://www.zcorp.com/

They have two vats with motorized pistons, one in which the powder to
be used it stored and one in which the model is built, as the model is
built its platform sinks and the powder hopper rises. The powder is
then transfered from one side of the platform to the next.

A video is worth 10million words:

http://www.youtube.com/watch?v=lDNLk7XvhRc

Pause it, let it download and then skip to 5:21

I don't understand a word they are saying but its the best video I can
find.

Someone in the past said a roller moved the powder, that can't be the
case it just wouldn't work, it would compress but not move, however
there is a roller but I THINK it is spinning quickly in the opposite
direction, its a bit hard to say so I'm guessing a squeegy pushes the
powder and the roller makes sure it is level by flicking off the very
top layer. Notice that the build area lowers a little before the
printing so the roller does not catch it and also that the roller
reverse direction and spins off the excess at the end of travel.

Can anyone confirm this or does anyone have any ideas?

Cheers,

Graham