the case probably acts like a heatsink?
i know you can buy fanless aluminum pc cases for a custom build and the cases are the heatsink (passively cooled)
not sure how hot they get though, if at all
like the cases these guys sell
A-Tech Fabrication Home Page
but i read that the macbook air does have cooling vents/intakes by the hinge
at least the older one
https://www.ifixit.com/Teardown/MacB...eardown/6130/1
oh here's a newer (2015) article talking about the mba
http://www.makeuseof.com/tag/macbook...-5-things-can/