Substantive editing

I recently found a nice little web page outlining the differences between copy editing, proofreading, and a third type of editing, 'substantive editing'. This third type of editing:

looks at both the content and structure of a manuscript as a cohesive whole. Does the story or argument flow logically? Are there obvious gaps in a certain area? Too much information someplace else? Substantive editing can involve re-ordering large chunks of text, removing text, adding text, and even rewriting

This quite accurately describes a lot of the work that Apus and I do (in addition to our copy-editing duties). We are both sub editors (or subeditors, or sub-editors if you will), which is a job title that seems to be confined to this side of the Atlantic. Is it possible that the 'sub' in 'sub editor' stands for 'substantive'? Probably not, but it's a nice thought, and it might be of interest to our American copy-editor readership...