I've looked at a number of previous discussions on the CV/SO divide for R questions - I'm not sure that any of those I've seen quite get to the following point:
There are now, I believe, getting on for 5,000 R packages - the astonishing growth representing the growth in interest and expertise in R evident here, as elsewhere, a diversity driven, in particular, by folks who are both experienced statistical pros and fluent coders.
There is often (not always, but often) an R function out there which will scratch the exact statistical itch that's bothering you right now, compared with the dozens of others that get only get close.
The problem is both that (a) the package-specific help is patchy and (b) there is no comprehensive source of information which matches R functions to itches - so tracking the right one down often depends on luck.
In many cases, what differentiates these functions is stuff that is 'under the hood' - that only those with a high level of expertise in both stats and R would easily grasp.
There are one or two sources of function comparison like this page for mixed models. But otherwise users are left guessing - and looking for help at SO or CV.
I've been monitoring answered questions with the R tag over at SO for a while: and they predominantly relate to function writing and data manipulation (plyr, reshape2, etc). They almost never talk about what's 'under the hood' of analysis functions like those in nlme and lme4 - I believe that such questions are deemed to be 'statistical' and therefore come under the remit of CV.
My question: is it generally agreed by those at CV that such questions are on topic? Clearly, CV is 'multi-platform' - although my impression is that, especially where examples (toy data, etc) are provided in questions or answers, R is the predominant language used.
On the other hand, what's 'under the hood' has (naturally enough!) a direct effect on the analysis CV-ers are doing. And those using SAS, Stata, etc. will surely have similar questions - so it wouldn't be a special privilege for R users.