Different games load the computer in different ways, as far as I know Minecraft uses the CPU quite heavily, making it work hard and increasing the temperature.
The best way to lower the CPU temperature is to remove the heatsink, clean it, clean off the old, grey thermal compound from the heatsink and CPU using a paper towel moistened in a cleaning solvent such as pure alcohol (not rubbing alcohol) and to apply fresh thermal compound before reassembling.
I think you'll find this useful:http://www.youtube.com/watch?v=8TbGz75_pV8
And this:
http://www.youtube.com/watch?v=SdyWDOf19J8
If you do this yourself be very careful about removing the heatsink, it will be stuck to the CPU, do NOT simply pull it, lift it with moderate force and twist left and right to free it, if you pull too hard it is possible to pull the CPU out of its socket and that WLL damage some of those tiny pins which are, from personal experience very, very difficult to straighten.