I have had a lot of mobile machines in the shop to try to fix after the user played games on it for months.
One machine had the CPU fan size on him and the machine froze on boot
tablets are completely passively cooled, so they can heat up and not be able to easily dissipate it
I guess I don't understand the word "passively" the same way you do. The Surface Pro 3 has a fan built in for precisely this reason.