Apple republished the Apple Watch video to YouTube with a couple of changes. The first is that the screen size in the renderings of the device is smaller in the new video—that makes the video match the way the device has looked all along on its website.
Here's a comparison of the screen sizes in the two versions of the video by Twitter user Khaos Tian:
Apple republished the Apple Watch Intro Video on YouTube?— Khaos Tian (@KhaosT) September 30, 2014
The new version of the video is on the left, while the old version is on the right.
The second change noticed so far is that the Glance screenshot has been altered. As again noted by Khaos Tian (via 9to5Mac), the Glance screenshot features a redesigned layout and a smaller icon to represent the weather.
The only UI difference I found between old and new Watch Intro video is for Glance. pic.twitter.com/mmp4ZXdUTS— Khaos Tian (@KhaosT) September 30, 2014
As above, the new version of the video is on the left, while the old one is on the right.
Here's the video in full. It still features Sir Jony Ive's narration and appears to be identical to the old one save for the changes above.