I think it goes beyond that. You have to give it credit. That much feat for a series of indie games. Then again, it's possibly the longest running series of indie/amature games ever made. Hell, there are so many game parodies featuring this series. One can understand the reason why it's popular, though.
I bet that deep down, ZUN is facepalming. He probably did not expect his creation to be this popular, and considering the result, he might not like it. He has some dignity, you know.