My guess is that a large part of the divergence relates to the fact that LWers and philosophers are focused on different questions. Philosophers (two-boxing philosophers, at least) are focused on the question of which decision "wins" whereas LWers are focused on the question of which theory "wins" (or, at least, this is what it seems to me that a large group of LWers is doing, more on which soon).
So philosophical proponents of CDT will almost all (all, in my experience) agree that it is rational if choosing a decision theory to follow to choose a one-boxing decision theory but they will say that it is rational if choosing a decision to two-box.
A second part of the divergence seems to me to relate to the toolsets available to the divergent groups. LWers have TDT and UDT, philosophers have Parfit on rational irrationality (and a whole massive literature on this sort of issue).
I actually think that LWers need to be described into two distinct groups: those who have done a lot of research into decision theory and those that haven't.
For those that haven't, I suspect that the "disagreement" with philosophers is mostly apparent and not actual (these people don't distinguish the two questions above and don't realise that philosophers are answering the winning decision question and not the winning theory question and don't realise that philosophers don't just ignorantly set aside these issues but have a whole literature on rational irrationality, winning decisions vs winning theories and so on).
This is especially powerful because the story is often told on LW as if LW takes rationality to be about "winning" whereas philosophers are interested in analysing our concept of rationality (and surely it's easy to pick between these). More accurately, though, it's between two divergent views of "winning".
For those that have studied more decision theory, the story is a different one and I don't know that I know the views of these people in enough depth to comment on them.
In Newcomb the outcome "pick two boxes, get $1.001M" is not in the outcome space, unless you fight the hypothetical, so the properly restricted CDT one-boxes. In the payoff matrix [1000, 0; 1001000, 1000000] the off-diagonal cases are inconsistent with the statement that Omega is a perfect predictor, so if you take them into account, you are not solving Newcomb, but some other problem where Omega is imperfect with unknown probability. Once the off-diagonal outcomes are removed, CDT trivially agrees with EDT.
Follow-up to: Normative uncertainty in Newcomb's problem
Philosophers and atheists break for two-boxing; theists and Less Wrong break for one-boxing
Personally, I would one-box on Newcomb's Problem. Conditional on one-boxing for lawful reasons, one boxing earns $1,000,000, while two-boxing, conditional on two-boxing for lawful reasons, would deliver only a thousand. But this seems to be firmly a minority view in philosophy, and numerous heuristics about expert opinion suggest that I should re-examine the view.
In the PhilPapers survey, Philosophy undergraduates start off divided roughly evenly between one-boxing and two-boxing:
Newcomb's problem: one box or two boxes?
But philosophy faculty, who have learned more (less likely to have no opinion), and been subject to further selection, break in favor of two-boxing:
Newcomb's problem: one box or two boxes?
Specialists in decision theory (who are also more atheistic, more compatibilist about free will, and more physicalist than faculty in general) are even more convinced:
Newcomb's problem: one box or two boxes?
Looking at the correlates of answers about Newcomb's problem, two-boxers are more likely to believe in physicalism about consciousness, atheism about religion, and other positions generally popular around here (which are also usually, but not always, in the direction of philosophical opinion). Zooming in one correlate, most theists with an opinion are one-boxers, while atheists break for two-boxing:
Less Wrong breaks overwhelmingly for one-boxing in survey answers for 2012:
NEWCOMB'S PROBLEM
One-box: 726, 61.4%
Two-box: 78, 6.6%
Not sure: 53, 4.5%
Don't understand: 86, 7.3%
No answer: 240, 20.3%
When I elicited LW confidence levels in a poll, a majority indicated 99%+ confidence in one-boxing, and 77% of respondents indicated 80%+ confidence.
What's going on?
I would like to understand what is driving this difference of opinion. My poll was a (weak) test of the hypothesis that Less Wrongers were more likely to account for uncertainty about decision theory: since on the standard Newcomb's problem one-boxers get $1,000,000, while two-boxers get $1,000, even a modest credence in the correct theory recommending one-boxing could justify the action of one-boxing.
If new graduate students read the computer science literature on program equilibrium, including some local contributions like Robust Cooperation in the Prisoner's Dilemma and A Comparison of Decision Algorithms on Newcomblike Problems, I would guess they would tend to shift more towards one-boxing. Thinking about what sort of decision algorithms it is rational to program, or what decision algorithms would prosper over numerous one-shot Prisoner's Dilemmas with visible source code, could also shift intuitions. A number of philosophers I have spoken with have indicated that frameworks like the use of causal models with nodes for logical uncertainty are meaningful contributions to thinking about decision theory. However, I doubt that for those with opinions, the balance would swing from almost 3:1 for two-boxing to 9:1 for one-boxing, even concentrating on new decision theory graduate students.
On the other hand, there may be an effect of unbalanced presentation to non-experts. Less Wrong is on average less philosophically sophisticated than professional philosophers. Since philosophical training is associated with a shift towards two-boxing, some of the difference in opinion could reflect a difference in training. Then, postings on decision theory have almost all either argued for or assumed one-boxing as the correct response on Newcomb's problem. It might be that if academic decision theorists were making arguments for two-boxing here, or if there was a reduction in pro one-boxing social pressure, there would be a shift in Less Wrong opinion towards two-boxing.
Less Wrongers, what's going on here? What are the relative causal roles of these and other factors in this divergence?
ETA: The SEP article on Causal Decision Theory.