What does "per blog" mean in "Mapping a subdomain with the Domain Mapping Upgrade costs $13.00 per subdomain, per blog, per year." ? Does it mean for each article submitted in my blog it costs $13, after subdomain mapping is done? Or is it specific to someone maintaining two or more blogs (like xyz.wordpress.com, abc.wordpress.com etc) with wordpress?
The blog I need help with is hubvirt.wordpress.com.