[Plugin: WordPress SEO by Yoast] Sitemap not being received by google webmaster

I have enabled the the XML Sitemap functionality. My XML files are being generated. I can manually upload them to google webmaster, however, I understand that the XML sitemap should be automatically uplload/discoverable by webmaster. This is not happening, why?

My website is http://www.electrocatalogue.com

Thanks in advance for your help.

PS – I have already posted this on the general support forum, so this may be a duplicate.

http://wordpress.org/extend/plugins/wordpress-seo/