alt Hacker News> Otherwise the air will escape to the sides.
Don't you want it to do that? The air goes upwards, hits the laptop surface, and travels outwards carrying the heat?
If it's sealed, I imagine you would get a very turbulent situation, possibly far noisier, but also one where I can't intuitively picture the airflow and expected cooling flow. I should note I am very, very far from an expert here ;)
There's a lot going on here, but the gist is that even a magnesium alloy laptop chassis is a rather poor conductor of heat (for a metal) and you really have to push that air through the machine to get it out.