a member in the G series thread posted in the rog forums to ask about this. Why is one the exhaust vent was partially closed?

apparently it was to prevent all the heat from going to the battery.

as quoted from the rog forum

"some of the right side is closed intentionally because that's where the battery is."

"Yes two fans and heatpipes - independently monitoring the GPU and CPU, output to one large, central vent. Aesthetically this vent is split in two, but the battery has to go somewhere, which is why it is blanked! Naturally the thickest point gives the most room for the 8 cell. Pop out the battery and see for yourself - it's absolutely not an error. They didn't make the vent smaller because symmetry is more visually pleasing. Technology doesn't adhere to human rules of beauty though - it's entirely functional.

If you watch the G55/G75 video you'll see the two cooling fans clearly - it's an accurate representation of the construction."

- MarshallR@ASUS