Matt Neuberg over at Tidbits has noticed an interesting behavior in Lion: Occasionally, apps running without an active window on will disappear from the Command-Tab application switcher, and sometimes disappear from Activity Monitor completely. The culprit is a new "feature" in Lion called Automatic Termination, which will shut down and quit any (compatible) apps that aren't active and don't have any visible windows. Of course, most official Apple apps support Automatic Termination.
As Neuberg notes, this is obviously a hat tip to iOS and its background processes, in which you "close" an app simply by navigating away from it, leaving the system to shut it down
