The Webmasters stackexchange is where webmasters hang out. The audience includes people knowledgeable in PHP, SEO, server issues, HTML (helpful with WordPress widgets), and lots of other areas that are relevant to admining a WordPress site.
On the other hand, the WordPress stackexchange is sparsely populated, questions don't get many views, and much fewer answers. The audience is small and narrow. Therefore, I find it questionable when a user intentionally asks a WordPress-related question on Webmasters and the question gets moved to WordPress (where it often just dies).
There is too much overlap, and the WordPress stackexchange is not a full-fledged experience. Moving questions there suppresses valuable discussion. All WordPress admins are webmasters. Therefore, let them be and see the title of this post.