Because:
I've become a BIOS-tweaking junkie (and sort of a pun there . . . ) I don't just "build computers" anymore; I absolutely have to tweak them.
There is overlap between CPUS & Overclocking and other forums, but we can intelligently discuss "other forum issues" as they pertain to OC'ing and tweaking -- here.
I'll second Borealis7's nomination, with a point being that there are a lot of "old hands" among our membership.
Also, this is a fairly serious forum, and Anand posts articles that directly bear on the discussions here. It's a valuable web-site.
Somehow, also, I just get an impression that the members here can be a bit more literate or knowledgable than posters elsewhere, but this shouldn't be taken to mean that other forums aren't just as informative.