I had a question here on Webmasters about tables, figures, and figcaptions. Today it was migrated to StackOverflow (https://stackoverflow.com/questions/12783679/a-table-in-a-figure-use-caption-or-figcaption). I'd like to know, why? It's a web development question, so was quite appropriate on this site.
Webmasters is for questions concerning management and administration of sites, generally as a whole. Questions involving actual code/markup (might, probably) belong on SO. Yes there's plenty of overlap(eg. analytics tends to stay here, and markup questions that're fundamentally about SEO) and threads fall through, but that's the very simple version. Often topics will just get evaluated case by case.
I have no idea why this only got migrated today; Paul will have to address that. I'm pretty sure I would have filed my vote back when I initially responded.