Larry's question is a doozy. 
 
The Internet Public Library says 
 
"When we get asked these questions about bestselling books, we always have to  
remind our patrons that their question is basically unanswerable. No one really  
knows which books have sold the most copies in history, because we simply don't  
have records that cover all of history! As such, any answer that we find is  
essentially just a "best guess" that is based upon estimates made by historians  
and other experts." 
http://www.ipl.org/div/farq/bestsellerFARQ.html 
 
At the bottom of the page, they recommend a Slate article that speaks directly to Larry's
question about how to define best sellers.  I thought you might find the lead interesting:
 
"These days, it seems as if half the books in bookstores have the word "best seller" or
some variant on the cover or the flap copy, as in "the best-selling author of ..." But
what does that mean? About as much as the phrase "original recipe" does on a jar of
spaghetti sauce."
http://slate.msn.com/?id=3504 
 
As for George's or Heilbroner's ranking, I think N is about as good as you're gonna get .
. .
 
Humberto Barreto