This statement is false, many manufacturers are beginning to see that giving warrenty, overclocking included, is a great selling point. Which it is, but we pay a little more for the hardware because of this. I don't know much about asus motherboard warrenties, as I'm not a fan of thier boards, but you should check it out and read what it states. Also, if the motherboard is gone it very hard to figure out what is wrong unless you swape it for another one to test out things such as your video card, sound card and ram. Are your fans even booting, LED lights on, on the motherboard? If not it may be the PSU. Sorry I didn't have time to read back.
The big downfall of overclocking is that it does void your warrenty. I have also wandered how much of a hassle would it be to return a part to the manufacture.