According to iojs, it looks like Open Source Governance is a fancy way of calling something open source and indulges in its principles. I could be wrong in interpreting this, but here's what the project says:
What is open source governance?
Open source governance advocates the application of the philosophies of the open source and open content movements in order to enable any interested party to add to the creation of the end product, as with a wiki document. Legislation is democratically opened to the general citizenry, employing their collective wisdom to benefit the decision-making process and improve democracy.
Nodejs says that they have over 300 contributors, as well as some 15 people on a "technical steering committee."
Bottom line, open source governance is implementing the open source concept and placing it into action. Both sites seems to have this, except iojs seems to talk about it more...