The main problem with that is that virtually all of Amazon's original target audience would have seen "Amazon File Server" and assumed it was a "File Server" li

The main problem with that is that virtually all of Amazon's original target audience would have seen "Amazon File Server" and assumed it was a "File Server" like every other "file server" they'd ever heard of, which either exported a file system such as NFS or Samba or used ftp or http to serve files-- and in the latter case, calling it a "file server" rather than an ftp server or web server would be rare. Since S3 was none of those things, they needed a different name.