Juin's response was to your question, why is BTX better.
I will field that question, if you dont mind?
All components inside your case generate some heat. Much of this is spread, or diffused by the mobo. Some is released into the air. With the processor at the top, it has less board around it to take the heat. It is also the recipient of much of the airborn heat. With the chip in the centre of the board, it will be better able to loose heat to the board, and will be better able to access cooler air. The chip is the most important component, so it should be given priority cooling.
To all you gamers who have dumped a lot of money into your video card, kiss it goodbye, cause it's not that important. Now it's turnaround time. Used to be that the graphics card gave heat to the processor, but now it's payback time.