While you are correct that this particular study offers no real evidence in the nature/nurture debate, my understanding of neuroscience is that the existence of early differences in gender-based behavior are so well established in the discipline that to publish on that result is no longer interesting to neuroscientists. What remains at this point is to figure out a mechanism behind that result. So the line of inquiry behind this paper is not so much "whither behavioral differences?" but rather "Given this large body of research over the past 10 years that demonstrates behavioral differences, what can we see in the brain that might be a mechanism for this result?"

If you are not familiar with that earlier body of research establishing behavioral differences, these studies might be a place to start, and then of course you can walk the bibliographies to find more.

http://www.psy.miami.edu/faculty/dmessinger/c_c/rsrcs/rdgs/e...

http://www.sciencedirect.com/science/article/pii/S1571891304...

http://scholarworks.umass.edu/dissertations/AAI9219513/

http://www.math.kth.se/matstat/gru/5b1501/F/sex.pdf

http://home.cc.umanitoba.ca/~dcampb/Campbell.InfantMetaALSex...

I recently came across a link to this book, which I have not yet been able to read: http://www.amazon.com/Brain-Storm-Flaws-Science-Differences/...

Published just a few years ago, it criticizes much of the research on sex differences, and from the reviews it makes a very exhaustive and compelling case. I'm curious if these are some of the studies it criticizes.

(I don't have an opinion on this either way as I have not been able to examine the evidence. But I'm very interested to see that there is so much controversy, even among scientists, on this issue).

I would encourage you to read criticism of this and Cordelia Fine's books, such as

http://www.biomedcentral.com/content/pdf/2042-6410-2-4.pdf

It has been argued that these authors have picked evidence they find disagreeable but fail to mention more solid studies.

I've read through "The Delusion of Gender"- http://www.amazon.com/Delusions-Gender-Society-Neurosexism-D..., where an Oxford, Cambridge, and UCL-educated Doctor of Psychology wrecks havok through Simon Baron-Cohen and his ilk's research.

It's a little boring, but systematic.

I'd rather trust a medical doctor to assess medical topics than a psychologist.

And exactly what 'nurture' are in-utero babies - the subject of the testosterone / interest tests - subjected to anyway?

You've read the book. Sum it up for us.