enigma1 - 2:33 pm on Mar 29, 2012 (gmt 0)
in my experience so far Google only seems to fetch CSS files once every couple of weeks or so. It's not something you tend to change that often after all.
So far I haven't seen the bot to access css or js in my logs. Also a site may have lots of different js or css scripts loaded depending on the page accessed. It's not that everyone uses the same files for all pages.