Thomas Boswell "gets" Moneyball more than most of his sportswriter comrades. But even he, along with many observers, misses the point to a degree.
In his generally solid review of the book and its ramifications, Boswell reduced the "Billy Beane method" to a list of a few factors. And his summary is technically accurate. But it misses the point, which Lewis and Beane take care to stress: that open-mindedness and the ability to search for and accept new evidence are more important than any given maxim.
And that is the best answer to questions like the one contained in an e-mail I received today from a friend:
"How many teams need to operate by those rules before the "overvaluing" stops? Once the A's, Red Sox, and Blue Jays are operating this way, can they all contend every year?"
As Rob Neyer says:

[T]he real key to Billy Beane's success, and also to his continued success (assuming that he continues to succeed): Billy's ahead of the curve. Let's assume, for a moment, that the A's draft philosophy works, and further that it's copied by a number of other teams. That's going to create a problem for those teams, because they'll all be competing for the same players, right?
And how do you solve that problem? By coming up with a new philosophy. And which organization is best-equipped to come up with a new philosophy?
I don't know. Maybe it's the A's, but the Red Sox are well-equipped, and so are the Blue Jays, and maybe the Indians and a few other teams. My point is that if the A's fall back to the pack, it won't be due to other baseball executives reading Moneyball, and it won't be due to other teams copying the A's philosophies. If the A's fall back to the pack, it will be due to a deficiency in management.

There is always more to learn. And the true lesson of Billy Beane's success, and of Moneyball, is that a willingness to learn and adapt will eventually trump a static list of rules.
Here are a couple of examples. The book describes how the A's used a system inspired by Wall Street's valuation of derivatives to calculate the defensive value of Johnny Damon as compared to Terence Long, and how while the difference was extreme by defensive standards, it was a) not as great as the difference in offensive value between extreme players and b) more efficient to make up the difference by adding more offense.
While a) is generally true, b) was a fact-specific conclusion. Another organization might take the moral of the story to be "always value offense over defense." In that case, they would likely overlook the occasional easy availability of an outstanding defensive center fielder who can't hit much. Someone like Chris Singleton, who now patrols center field for Billy Beane's Oakland A's. In that case, his defensive abilities were undervalued, and the A's took advantage of the inefficiency.
Here's another thought. As I've noted before, the biggest flaw in the book is the omission what the A's are doing with their pitcher development. Supposedly they haven't had a major surgery in their organization in years (though I haven't checked that assertion) - by contrast, the Yankees should've gotten a group discount on "Tommy John" surgeries over the last couple of years. Their program is based on a combination of avoiding high school pitchers, constant work with mechanics based on an institute run by Dr. James Andrews (the surgeon who does most major pitcher surgeries), pitch counts, and other things. It's still unclear if they've discovered the secret to pitcher development, but it's looking good.
What if they really have learned the secrets to avoiding pitcher injuries? Maybe in a few years the A's will decide they should shift to preferring high school pitchers - that way, you keep them in-house for longer and avoid the risk that college coaches will shred their arms. That will shock all those who have read Moneyball and taken from it the message "high school pitchers=bad." But the A's may be ahead of the curve again.