I wonder if Notch doesn't take on big projects anymore has more to do with him affording not to deal with the stress and patience it takes to deliver a big project. I think it is the same problem that many in the post-success stage have. Look at some of the greatest bands in recent history. You don't see Led Zeppelin, Rolling Stones, Eagles etc creating at the same level they used to despite being the same creative people. Another example are actors like Al Pacino, Robert De Niro, and Harrison Ford. I just don't think they have motivation for money, more fame, or that self-high of doing something great yet again.
If you didn't have to worry about money would you still work on what you are working on now? At the very least, it sure would make it easy for me to say fuck it when the work hits a low point.