There were a few numbers thrown out during the session, none of which exactly matches your question, but might be closer to what you want to know anyway.
He estimated that an O'Reilly book can be expected to net around $20K - $70K for its author (I can't remember if this was "the first year" or "per edition").
For a single title, 60-70K books sold per year is high these days -- it used to be low, but for the last several years the market had been dropping 20% per year or so. Thankfully this has settled down so that this year is about even with last year.
The O'Reilly record holder is Java in a Nutshell, which has sold 600-700K copies in its life. He guessed that only K&R and perhaps Stroustrup had sold more copies in the programming industry.