The question remains also why a section so heavily moderated such as the mining section gets three mods whereas things like bitcoin discussion gets 1 (and that's a global mod so it doesn't really count) and project developement has no mods...
It explains why the Mining board isn't a spam fest.
At the time of posting this comment, of the 39 threads on the front page of the Mining board, 31 of them are locked. Any thread that is low quality or spam is trashed, and any thread that has had OP's question answered is locked. OgNasty's thread is 14 pages, but there isn't a single spam post in it - that would be impossible in Bitcoin or Altcoin Discussion. Dedicated board mods not only help to keep a board clean (obviously), but they also free up the likes of hilariousandco and other global mods to deal with more important issues than deleting garbage posts.
There's probably no reason other than that's just how it came to be. That board probably doesn't
need three mods, but there's certainly some other boards that do need
at least one and Bitcoin Discussion is one of them. In fact, I'd say most sub boards probably need at least one dedicated mod. It just frees up workload and saves everything being pilled up for Globals. Moderating Bitcoin Discussion (or trashing all the shit threads in there) would probably be a part-time job in itself, but until we get a couple of dedicated mods there and clamp down on the root cause of the spam (ICO campaigns) then nothing much will change.