I have not actually seen the video, but I do know that there is a controversy that this was staged. I know that a LOT of tech sites can prove that Toms hardware is a biased site (like the benchmarks that he shows does not match his conclusion, or using tests that favor one processor over the other, amd vs intel).
If I remember correctly, the video was staged because you would never get to the point of seeing flames from a processor overheating. This is not to say that you won't cause severe damage/melting in the extreme case that is presented by that article/video. The whole controvesy was that he "rigged" the system to overheat in a way that would not be seen if this was an actual system (turned off the motherboard auto-shutoff, ranning the chip without the heatsink and fan, instead of just showing what happens when the fan dies but the heat sink still works).
As to your question about clock throttling, the Athlon 64 does do this, I believe that it now has an internal (on chip) thermal diode, like the intel chips.
If I can dig up some links about the "controversy" surrounding the tom's hardware video I'll post it here.
Edit: here are some links regarding this controversy. I think that they show enough doubt as to whether or not the testing was completely accurate
http://www.tech-report.com/news_reply.x/3057/0/
http://www.geek.com/news/geeknews/20...1029008570.htm
http://club.cdfreaks.com/showthread....threadid=60929