[henesy]

Yes, /bin is a directory where the bind[1] command can be used to multiplex/union other directories on top. The / directory in general is built this way as a virtual top directory, with the disk root being stored on /root and being bound over /.

Platform-specific files are stored in /$architecture and binaries in /$architecture/bin. Shell scripts are stored in /rc/bin. For the home directory, traditionally, this style is reversed so your shell scripts would be in $home/bin/rc.

The namespace for any process can be enumerated, so in my default shell, I can see which directories are currently bound (and how) on /bin:

  tenshi% ns | grep 'bind' | grep '/bin' 
  bind  /amd64/bin /bin 
  bind -a /rc/bin /bin 
  bind -b /usr/seh/bin/rc /bin 
  bind -b /usr/seh/bin/amd64 /bin 
  bind -a /sys/go/bin /bin 
  bind -a /usr/seh/go/bin /bin 
  tenshi% 

[1] http://man.cat-v.org/9front/1/bind