Um... do you know what a copy-editor does? He improves formatting, style, and accuracy of the text. He is not concerned with the substance of the text. That's what you have an editor with knowledge about the subject matter for. One is not a substitute for the other.
It would be a miracle if the absence of a good copy-editor won't result in a lot of errors going uncorrected.
Hans
Many game designers have found that for game purposes, the copy editor MUST be a gamer, and must understand the game... because when they don't, they have a tendency to correct standard notations into unintelligible mush. One game's proof copy came back with every "1D" reference replaced with "ten" (I saw the draft for that one). Another, all the tables were eliminated by the editor, who didn't realize that they weren't duplicated. Those are the worst two I've heard of, but many lesser such errors have been induced by well meaning but ignorant copyeditors.
SJG is unusual in that it has a trained copy editor on staff - most game companies have it as a duty, but not someone specifically trained for it, because of the issues involved in needing to grasp what is being presented in order to ensure it is presented intelligibly.
Bringing an outside copyeditor up to speed in the timeframe Marc had set was not likely to be practical. And the ones that could be trusted to do it right would already be busy with projects.
Thor Olavsruud has discussed at lengths the needed skillset for a game copyeditor. He's the editor for Burning Wheel HQ, and works as a collumnist for a business mag.