Why does my Macbook Air get so hot when playing even a simple game? Basically, even small games like Rogue Legacy, Battle World: Kronos, Magicka, Crusader Kings, etc. These are not graphic intensive games, yet the laptop reaches temperatures over 90 C. However, this doesn't happen with Hearthstone. So, out of curiosity, why does this happen? Will it happen with a current-gen iMac?
Although the games may not be graphically intensive, they may still be intensive on the CPU, and it is likely the CPU temperature you are seeing rise. 

A way to check this would be to use Activity Monitor.app while playing a game to check out the CPU usage. Or if you are comfortable and able, SSH into the Mac while playing the game and using the top command to check.