I could do, but the way it's built is using a master array in the page creator file. To add a feed, I just add the new feed and favicon location into the array. Storing the images would mean more work each time a new feed is added.
Having said that, CSS Sprites is something I don't know much about and will be looking into.
It'd take a tiny bit more work on the frontend, but instead of saving the favicon location, you could save a data-uri of the favicon image. That would then completely eliminate all of the external HTTP requests.
Having said that, CSS Sprites is something I don't know much about and will be looking into.