different between unicorn / unicorn_rails

$ unicorn_rails -h
Usage: unicorn_rails [ruby options] [unicorn_rails options] [rackup config file]
Ruby options:
  -e, --eval LINE          evaluate a LINE of code
  -d, --debug              set debugging flags (set $DEBUG to true)
  -w, --warn               turn warnings on for your script
  -I, --include PATH       specify $LOAD_PATH (may be used more than once)
  -r, --require LIBRARY    require the library, before executing your script
unicorn_rails options:
  -o, --host HOST          listen on HOST (default: 0.0.0.0)
  -p, --port PORT          use PORT (default: 8080)
  -E, --env RAILS_ENV      use RAILS_ENV for defaults (default: development)
  -D, --daemonize          run daemonized in the background
  -l {HOST:PORT|PATH},     listen on HOST:PORT or PATH
      --listen             this may be specified multiple times
                           (default: 0.0.0.0:8080)
  -c, --config-file FILE   Unicorn-specific config file

      --path PATH          Runs Rails app mounted at a specific path.
                           (default: /)
Common options:
  -h, --help               Show this message
  -v, --version            Show version

$ unicorn -h
Usage: unicorn [ruby options] [unicorn options] [rackup config file]
Ruby options:
  -e, --eval LINE          evaluate a LINE of code
  -d, --debug              set debugging flags (set $DEBUG to true)
  -w, --warn               turn warnings on for your script
  -I, --include PATH       specify $LOAD_PATH (may be used more than once)
  -r, --require LIBRARY    require the library, before executing your script
unicorn options:
  -o, --host HOST          listen on HOST (default: 0.0.0.0)
  -p, --port PORT          use PORT (default: 8080)
  -E, --env RACK_ENV       use RACK_ENV for defaults (default: development)
  -N                       do not load middleware implied by RACK_ENV
      --no-default-middleware
  -D, --daemonize          run daemonized in the background

  -s, --server SERVER      this flag only exists for compatibility
  -l {HOST:PORT|PATH},     listen on HOST:PORT or PATH
      --listen             this may be specified multiple times
                           (default: 0.0.0.0:8080)
  -c, --config-file FILE   Unicorn-specific config file
Common options:
  -h, --help               Show this message
  -v, --version            Show version

config/unicorn.conf.rb

# See http://unicorn.bogomips.org/Unicorn/Configurator.html for complete
 # documentation.

-rails_env = ENV['RAILS_ENV'] || 'staging'
+rails_env = ENV['RAILS_ENV'] || ENV['RACK_ENV'] || 'staging'
Add a comment to this line
 # Use at least one worker per core if you're on a dedicated server,
 # more will usually help for _short_ waits on databases/caches.
-worker_processes rails_env == "production" ? 4 : 1
+worker_processes (rails_env == "production" ? 4 : 1)

 # Since Unicorn is never exposed to outside clients, it does not need to
 # run on the standard HTTP port (80), there is no reason to start Unicorn