I understand he's forgone the amount of wealth he could have accumulated by just working in the software industry in the name of his cause, and that is laudable. However he thinks everyone should do this despite the greater burden they'd have to shoulder. All the people he tells shouldn't be making non free software so they can support themselves and their families are not going to be given free lodging by MIT.
However your comment above said he lived comfortably off the income of his own celebrity. We would have to twist the word income here for a bit to cover this kind of situation. The comfortably part is also a bit questionable, but I guess living at the office can be comfortable to some people. The description just didn't fit the situation that well, which is why I wrote the above comment.
For most part of his life he was living in his office at the university, technically homeless. After that period he lived in a home designated by MIT, possible because they got tired of the building code violation of having a professor living in his office.