Yes, gaming is very strenuous for a computer, both for the CPU and GPU. Both the CPU and GPU generate heat when pushed, causing the fans to kick on to full boar and to not stop until the stress is ended and the computer has cooled. The aluminum case the PB and MBP have also works as a secondary heat spreader, meaning that the case gets hot to the touch but is actually improving convection.
There are several things one can do to improve heat dissipation. The simple, passive, thing to do is keep the vents clear. After that you can elevate you computer on a stand that leaves plenty of room for air circulation. If you want to actively cool your computer, you can get a fan or even and stand with a fan. The ultimate solution it to set up your computer in a walk in freezer. Although, I won't let your computer's temperature drop below freezing, as that can be detrimental too, so you'll need to keep playing WOW.