i think the author follows a similar idea as Tim Berners-lee with this paragraph in the "Giant Global Graph" article:

"So the Net and the Web may both be shaped as something mathematicians call a Graph, but they are at different levels. The Net links computers, the Web links documents."

published at http://dig.csail.mit.edu/breadcrumbs/node/215

so, if it is something that is not a html document that can can be reached via a hyperlink is not part of the web but it just uses the internet.