This was one of those few cases were the split was necessary. You could ship a very small initrd via bootp (or floppy, or much later, CDROM), and once it came u

This was one of those few cases were the split was necessary. You could ship a very small initrd via bootp (or floppy, or much later, CDROM), and once it came up it could mount /usr over NFS. In case there were problems with the NFS mount, you still had some utilities in /bin for troubleshooting. The alternative was 'remote root NFS', where the root filesystem itself was NFS, and any network problems hosed the machine entirely. Trying to attach some alternative troubleshooting tools into a thin-terminal, or customize the bootp server to boot a troubleshooting image just for the one malfunctioning box, was a lot more painful than just shipping troubleshooting tools in /bin.