I've never had an experience as bad as that shown in the video on my Nexus One, a phone older than the Nexus S. It looks like he might have Flash installed - that's a mistake, as the Android browser's "on demand" option for plugins doesn't disable Flash reliably. Apart from that, it's clear that Android does not render to a GPU texture and scroll around, and this makes the iOS browser feel a lot slicker, but the difference between it and my N1 is small - and the iOS approach frequently leaves large grey blocks when scrolling quickly that need to get redrawn, because GPU texture size is limited.
Here's a different video, to demonstrate (Nexus One without Flash vs iPhone 4 running iOS 4): http://www.youtube.com/watch?v=4gZiSG3TmdY