I didn't intentionally choose today's Scourge theme. Really. These things just happen. That Dragon-specific one I did all that time ago? I didn't plan that, either. I'm just awesome enough that these things come together all by themselves. Yep. It's my pure, radiant awesome.
What? What do you mean current game content dictates what topics are hot or not? Pssh, that's crazy talk. That can't be it. It's all me, y'all.
"Who built Icecrown Citadel and the accompanying structures? Did Arthas build it after he became the Lich King, or was it already there?"
The massive Saronite structures that make up Icecrown as it is today is all fairly new, from what I understand. Most Scourge architecture is based on Nerubian architecture (as you can see in Ahn'kahet) but the Saronite structures in and around Icecrown seem more styled after the Lich King himself. You certainly didn't see that stuff in Warcraft III either, but I suppose that's not always a good indicator.