Lots of apps implicitly put images in a "never changes after the initial render" category. Retrofitting what is effectively a movie format into that can be interesting.

Some people who started browsing the web back in the days of GeoCities also reflexively disable GIF animation in their browser preferences.

In this case it's the RSS feed itself, not the reader. The image in the feed is just a static PNG:

http://imgs.xkcd.com/comics/frequency.png

Which did somewhat confuse me as well until I looked at the actual website.

As far as I'm concerned, displaying animated GIFs is a bug not a feature (its use here notwithstanding), and I'd report it as one if I thought the Chrome team would take bug reports from the likes of me, so if your viewer doesn't have that bug, be happy!