The mystery is solve. Thanks everybody.
Good lord, there are + buttons??
I never knew! So all the subforums are hidden by default?? No wonder people keep posting HTML or CSS-specific stuff in the general Web Design forum!!
I usually go to the breadcrumb "Forum Index" where the sub-forums are hard enough to see (with my old specs anyway).
But if you go to the top nav bar "Forums" you'll see
Ah. I've never used that page to go to forums, I use that page to go to featured threads or quick overview what's new.