I love your posts, Nilly. Dr Horrible, to me, is about five things: being outside of society, the fear of being alone, the difficulty of making a connection with somebody, the imbalance of society and Captain Hammer's penis. It's really typical Joss Whedon themes - which unsurprisingly I'm drawn to - with the added bonus that it's really well shot, and oh yea - it's really good.
So, creatively, I think it works incredibly well. From a business point of view, too, it's worked really well. It's basically the first example I think we're going to see of a successful indy produced web series, without any corporate investment. Which is very much not status quo.