He saw Silicon Valley celebrities such as John Doerr grab the limelight as they proclaimed the Internet to be the greatest legal money engine ever created.
It is the engine that created some of the great advances in human health in this century: treatments for deadly infections, for heart disease, for depression.
Newell doesn't directly refer to the in-development engine as "Source Engine 2, " so it's possible (albeit unlikely) that he's referring to a separate engine altogether, or (even more unlikely) Valve has more than one game engine being created.