Because a complete rendering of the page includes fetching /favicon.ico.

If there even is a favicon... and if a .ico file is considered an "image".

If there is no favicon... There'll still be a request, it'll just 404.

Every modern browser I know of automatically tries to fetch favicon.ico.

Good point. I suppose it's presumably async with respect to the render anyway. It looks even more nuanced on pages that have an iframe [1] (though presumably that's not the case here).

[1]: http://stackoverflow.com/a/13416784/149428

On the other hand you only need 2 if you use css image sprites.