That's what I thought as well, until I read this post from "Fake Steve Jobs". Not the most reliable source, obviously, but he does seem to have a point:

But, see, arguments about national averages are a smokescreen. Sure, people kill themselves all the time. But the Foxconn people all work for the same company, in the same place, and they’re all doing it in the same way, and that way happens to be a gruesome, public way that makes a spectacle of their death. They’re not pill-takers or wrist-slitters or hangers. ... They’re jumpers. And jumpers, my friends, are a different breed. Ask any cop or shrink who deals with this stuff. Jumpers want to make a statement. Jumpers are trying to tell you something.

Now I'm not entirely sure of the details, but if it's true that all the suicides in the recent cluster consisted of jumping off the Foxconn factory roof, that does seem to be more significant than just 15 employees committing suicide in unrelated incidents. In fact, it seems like it might even be the case that there are a lot more suicides than the ones we've heard about, and the cluster of 15 are just those who've killed themselves via this particular, highly visible, method (I'm just speculating here).

I'm not sure what to make of this - without knowing more of the details its probably impossible to say what's going on. But the basic point seems sound: that the argument about being below national average suicide rates doesn't really hold up if there's something specific about a particular group of incidents that makes them non-independent. As an example, if the members of some cult commit suicide en masse, you can't look at the region the event happened in and say "well the overall suicide rate for the region is still below the national average, so there's nothing to see here"