if you go TOO fast down it will loose the whole feel and would be nothing more than strumming a bunch of notes.

but ye, and can still be considered sweeping without the upstroke, but without the up your losing a whole lot of future possibilities, doing different note shapes/combinations on the way up (little different from wat you did on the way down) adds a really nice feel and being able to go down AND up is the key to being able to master the art of sweeping arpeggios.