Yeah, but if they connect as a player anyway, then the same penalty is applied. =)
The difference is that players stick around, so you only get the penalty once. Every observer that desides to Check You Out will get a fesh copy of the image assets. So if 10 people simultaneously decide to observe your game, you'll be uploading all of you image assets 10 times. Then a couple minutes later another 3 join, 7 of the first disconnect ... ad infinium
You could designate an observer quota that is set by the server/GM...
Default 10, then when it's full, a message appears indicating it's full but may be available in the future, then when someone drops, it's open