I always found a notion of a forum called "Linux, OS X and Open Source" quite amusing. OS X has about as much in common with open source as SGI had with freeware (when SGI launched their sgifreeware site it soon became industry jest - sort of "we'll finish this project shortly after Duke Nukem Forever, or Daikatana is launched" equivalent - "It will be free of charge like sgi freeware" meaning "you will get free lynx browser for £53,000 machine, running £4000 OS with £11,000 basic annual support contract on it, yupee"). Anyway, I digress. Discussing MacOS in Linux forum belongs here as much as discussing smartphones would belong in Windows forum, really. I don't think relatively low traffic is caused by lack of interest in Linux on these forums but, it's just that you don't expect anyone to discuss Linux in what de-facto became Intel based OS X fanclub. As simple as.
Let's face it, I know going through 2000 or so threads to separate them might not look like fun to moderators but it's not like giving the two OSes individual forums would require extra vBulletin license. On the other hand, if it doesn't work merging two forums is really easy. "Optical Storage" is low traffic forum and could easily be amalgamated into one big "Drives" forum, but everyone can clearly see the need for it, meanwhile mixing fox hunting and cooking section on the basis of "oh, they both contain meat", or in other words Linux with OS X just bacase there is a shell and terminal in both is percieved like a good idea?
It's not as much inconvenience as just odd.