This only applies to files that are /actually hosted on the amazon servers/, which is just select files Badspot collected and put up there. The vast majority of files are still served directly from the host.
blockland.s3.amazonaws.com contains 100030 files. Are you sure about this?
The 30 files are probably things badspot put there manually, like the installer - the other 100k are the most recently used resources for servers.
After loading the file manifest on a server you have two stages of loading files. First all the ones found on the cdn (single progress bar) and then the ones that have to be requested from the server (two progress bars). I'm not sure what makes a server decide whether a file goes on the cdn though. Music files are never uploaded to the cdn I think.