Why Don't Publishers Check Facts

The Economist pens one of its customarily acerbic book reviews in which it notes an extraordinary number of basic errors:

The trouble starts when Ms Moyo ventures into economic analysis. In comparing America's economy with China's, for instance, whether you convert yuan into dollars at market exchange rates or after adjusting for purchasing power matters a lot. Measuring at purchasing-power parity makes the gap in GDP and living standards look narrower. This explains a great deal of the difference between two sets of figures that Ms Moyo cites. Yet she does not mention it.
This is basic stuff. Much else in elementary economics also gets mangled here. Governments usually manipulate exchange rates to make their currencies artificially weak, not strong. In the Keynesian national-income identity, G represents government spending, not the budget surplus. The idea of a special tax on sports stars' incomes to discourage youngsters from unrealistic aspirations is intriguing, if contentious; suggesting that the two groups might bargain away such effects is absurd.
There are some puzzling omissions. Ms Moyo rightly complains at the exclusion of big emerging economies (except Russia) from the G8. She celebrates the strengthening of their diplomatic muscles. Amazingly, she seems not to have noticed the prime manifestation of this: the rise of the G20, which since 2008 has eclipsed the smaller, rich-country club.
Worse, Ms Moyo commits some jaw-dropping factual errors. General Motors, she writes, was bought by Fiat, "an event unimaginable just a couple [of] years earlier". Yes, and it still is: the Italian carmaker did not purchase GM, but a 20% stake in Chrysler, recently increased to 25%. France gets "almost 20% of its electricity from nuclear sources". The OECD says the figure is close to 80%.
Ms Moyo's editors are as bad as her fact-checkers. If they couldn't spot the analytical flaws, they might have done something about the stylistic ones that range from curious analogies to long phrases in parentheses. Endnotes are used almost at random.

How does something like this happen?  Online, of course--people write quickly, and they often work from memory rather than looking up every fact.  It is, as any writer can attest, startlingly easy for a bad fact--like Fiat buying GM--to insert itself so thoroughly into your consciousness that you don't even know you ought to look it up.

But this is what fact checkers are for, and I don't understand why book publishers don't have them.  They cost money, to be sure--but not that much money.  Sadly, there are a lot of experienced magazine people around right now who could be got at very competitive freelance rates.  A quarter of a million dollars a year would get you the world's finest staff of crack fact checkers; quite a bit less money would prevent embarassments like this book.  It might have even headed off the Arming America disaster, if a fact checker had noticed that the figures in his, er, smoking gun table, didn't add up.

Presumably the answer is that it isn't economic: readers don't care, and indeed rarely learn; there's no money in preventing the occasional catastrophe like Arming America.  But then one must turn the question around: why do magazines like The Economist, the New Yorker, and yes, The Atlantic, employ fact checkers?  Our readers are the potential consumers of books like the one that the Economist is reviewing; do they care less about accuracy in their books than in their magazine articles?

Not that anyone at The Atlantic thinks about it that way; we employ fact checkers because it seems like the right thing to do.  But why does this ethic prevail at so many magazines, and at no publishing house?