Well I thought that, but I wouldn't but a wet towel on any part of my system in fear of it shorting, and I would imagine even if the paper towel were wet, it would still be able to short and fry the video card
If you notice in the pictures (with the paper towels) the power supply was jumpered ie the system wasn't running only the pump/fans so even if it did leak it would not have hurt anything, the paper towels were just to easily identify any areas that may have a leak.