I doubt that this is the case. I got the PS3 version, and the shadows dither like hell. If the upscaling is able to remove the dithering, it should do the same on the shadows.
I can confirm this, I'm playing the PS3 version at 720p (selected on xmb of course) in a 1600x1050 Samsung 226BW monitor and the shadows have dithering. I think I've only seen dithering in these shady situations (hur hur I kill myself) though.