Forget the stigma that videos have to be paired with audio. A video is a convenient means of making a moving picture. They're easier on bandwidth, higher quality, and more flexible.
I like HTML5 vids-as-gifs, but gifs still have some upside. Gifs are still more portable and distributable. In this instance, bandwidth and probably negligible given that there's so few frames in the gif.
Portability isn't a concern here. Realistically, an extremely small fraction of your users have unsupported browsers. Maybe some forums won't let you embed video, but if you're building a product site you have the freedom to use whatever you please.
Wouldn't it be nice if your marketing wasn't covered in artifacts? Every GIF on this page is full of artifacts. Would it be valuable for users to be able to pause and appreciate a feature they think is neat?
It's high time for GIFs to die. HTML5 video is a worthy replacement.
I was also thinking that it would be negligible for slideshow gifs, but the iPhone example went from a 1.5MB gif to a 500KB WebM. Using video means you also remove the 8-bit color restriction that is imposed on gifs. (without hacks, at least)