Actually, it's hard to claim any figures show that. What they show is sales to comics stores. The stores decide what to stock and in what numbers, so again it's taken out of the direct hands of the readership. Also, it's impossible to tell with the Amazing sales. Maybe 40,000 readers DID drop the book post-BND. Maybe the book did what it was intended to and attracted new readers to replace them. Not likely, but still...
And the sales thing is flawed, frankly. There's plenty of anecdotal evidence that people didn't pick up the Batgirl mini because they disliked the direction DC were taking the character in. What that translates to is poor sales and poor sales demonstrate a lack of audience for that character. But they don't, of course. What they demonstrate is a lack of audience for the character written the way they were, a disinterest in the artist and countless other reasons why people don't pick books up. So the readership avoiding a certain title don't give the clear message you think they're giving.