Remote Management vs. Screen Sharing? What is the difference between enabling remote management and enabling screen sharing?

Apple's support article, http://support.apple.com/kb/HT4715, says:


  If the Apple Remote Desktop administrator authenticates with a name
  that is different from the user logged on at the remote computer, the
  following applies:
  
  
  If the service was enabled by turning on Screen Sharing, the screen sharing user is presented with the option to request sharing access
  from the user logged on at the display.
  If the service was enabled by turning on Remote Management, the screen sharing user can simply choose to share the display.
  The screen sharing user can always choose to log in to their own session.
  
  
  ...


It also states:


  If the remote computer's display is at the login window, the Apple
  Remote Desktop administrator will simply share the display. This is
  equivalent to how screen sharing works in earlier versions of Mac OS
  X.
  
  A third party VNC viewer will always be connected to the login window.
  If the login window is not on the display, a new login window is
  started that is not shown on the display. The screen sharing user can
  then log in with any valid account on that computer.


So, I presume that it is using the same protocol (VNC) underneath and just behaves a little different depending on which option you enable.

What is Apple's remote client?  Is it the Screen Sharing app  in CoreServices (/System/Library/CoreServices/Screen Sharing.app) or is there something else I might have missed?

Lastly, what is the Mac App Store "Apple Remote Desktop" product ($80, http://itunes.apple.com/us/app/apple-remote-desktop/id409907375?mt=12) and how does it differ from the above?

Thanks!
By default, Mac OS uses VNC combined with a few extras (e.g. auto-discovery via Bonjour) when you use Screen Sharing, and in most cases this is all an average user needs.
For system administrators however, there is usually a need for more control over the computers they support; therefore Apple provides "Apple Remote Desktop" (ARD) which offers a lot more control mechanisms (like terminal sessions, remote installation of software, remote shutdown, remote execution of automator scripts) and this is possible with groups of many computers at the same time. For this feature to work, SSH and remote management needs to be activated.

So in short: Screen Sharing is roughly equivalent to VNC, while Apple Remote Desktop is a "high-end" remote administration software which requires "Remote Management" to be turned on. There is also a difference in how incoming screen sharing requests are handled: with "Screen Sharing" enabled, if an observer connects with a user account that's different than the one currently logged in and clicks Share Display, the user needs to confirm before the screen is shared. With "Remote Management", the screen is immediately shared without a prompt appearing.