Clearly, nurses miss that there are Groups and among them are Nurses..
So? They are nurses, they will probably use their medical skills to survive out here in the open. :-)
But seriously, the reason you see a growing number of nurses is because the company that owns a2k happens to own a lot of websites in the nursing industry (it's the main niche we make a living in, and it currently supports us so that we can do fun projects like a2k on the side). You might as well get used to them because they may be joining us in larger numbers (we own several other nursing communities that we may also one day merge here) and because nurses aren't all that bad once you get over their whole nursiness (nobody's perfect, you know).
Edit: but your general point about the group navigation is a valid one, and one we have a neat idea on how to change it... once we shore up our core nursing businesses a bit.