Why do you think those are animated gifs? They've not. They're more likely 3gp, avi, flc, or something else. I know, I read this page:

http://www.121movies.com/technology.html

However, that's just the parent company's website. If you go to

http://www.movietexts.com/page.asp?id=1&page=home.aspx

You can actually look at some of the real ones. In which case you're looking at flash animations, not gifs.

Also, what does this have to do with game development?