It is interesting that some of you refer to warm water diving as being a subset of cold water diving. While I see how this idea formed- I find it to be nearly opposite. Warm water started quite a bit of the original recreational diving- and most of the skills that I teach students are archaic left-overs from warm water diving that sometimes has very little to do with cold water diving or skills you would use while cold water diving. For example: there is a huge difference between removing a weight belt in warm water vs. cold- the amount of lead is normal different, as well as the amount of gear you have to manuever around also.
With an 8lb belt, I just take the thing off, then swirl it around my back and put it back on again- while with a heavy cold water belt, (even with weight integration,) I have to lay the thing out in front of me and then twist into it. There are many other "basic" open water skills that sometimes need to be modified for cold water certifications.
I HATE the constant ego of diving- my idea of all of this is that if a diver is comfortable, safe, and having fun- as well as knowing what their limits are on any given day, they are a good diver.
I get tired of the "I'm a better diver than you are" mentality- this despite being a cold water diver myself. Do I love cold, low vis diving? Yes. Would I find it even more special to be out in warm water looking at something pretty I've never seen before? Heck Yes. Am I somehow not a "good" diver if I opt out of dives that I have done plenty of times before in lue of watching other people have a good time? I don't think so- I suppose I'm just interested in some new places, I get bored if I fall into the same dive site a million times in a row, especially one that has really only one diveable pattern.
So- to sum my .02 up- I think that cold water diving emerged from warm water skills and equipment that were simply adapted into working in the different enviornmental conditions.
Keep in mind, there are many, many reasons that cold water divers make up less than 5% of the total number of divers... and some people don't consider it cool that you dive in low vis, current or very cold conditions- just like there are many cold water divers that wouldn't do a shark dive easily or manage to stay far enough off the bottom on a reef to not harm the coral itself.
Each to their own... I say everyone just do what makes you feel good.