The way i`ve personally always thought about it is that if it is a backdoor/trojan like Sub7 you can install it on the "victims" computer without having to install or set it up locally. But genuine remote managment types like WinVNC you have to either install it or set it up locall. E.g. in WinVNC you have to set a password for the connection locally on the computer before you are able to connect.
Some people might diffrent opions but thats just how i`ve always looked at it.