@evildictaitor: Leaving aside the almost inevitable race conditions in determining that, it's still deleting files based on some external factor that is out of the control of the OS. What if the file on the server has been momentarily deleted with the intention of putting a replacement in? Or if there is some temporary issue that makes the file appear to have been deleted?
There's no race-condition here. If the file exists the shortcut stays. If it doesn't it goes. If the file appears slightly after the shortcut went away, well the shortcut wasn't pointing to something so it deserved to die. If the file disappeared after choosing to keep the shortcut, well you're no better off than before where the shortcut points into the ether.
Look, I'm not saying deleting shortcuts without a prompt is a good idea - I'm just saying that it's a valid action for the OS to take. The sole purpose of a shortcut is to take you to a target file. If that file isn't there then the only purpose of the shortcut has vanished, and hence leaving the shortcut around clutters up the folder. The reason will be that uninstalling programs often doesn't delete the shortcut files they inevitably dropped on the desktop during install, and this was an attempt to stop your desktop becoming a shortcut cemetery.