True, it's not. Unless you don't know to do that, post something because you only searched in one place, then get hit with 'you posted something already up' messages. Which happened to me about a month ago, although I think a contributing factor in my case was insufficient tagging.
I'm no webmaster either, so I can't suggest how merging these databases could be done or if that's even possible. But maybe somewhere in the site rules there could be a bit about searching each section of the site for content you want to post before doing so. And that would give folks a clue that they'd need to do that if they're also looking for something specific.