and all the dust will fall to the bottom, lets shut this case and have it run 24/7 for a year without opening the case... if it havent stoped working or your house burnt down its a miracle. it is idiotic to place the power supply in the bottom of the case, period.
Many modern tower cases now house the PSU at the bottom of the case (with a dust filter). It is not the PSU's task to remove heat from the tower, but that is the task of the exhaust fans/radiators. There's much logic in that.
Really.
The Corsair Obsidian, for example.
Or the
Fractal Design R2.(or perhaps, I'm just missing all the 'witty sarcasm' in this thread).

Steve