The numbers reported only count Google subscribers – but it’s interesting that Google are now tracking this information (makes me wonder how long it’ll be before subscriber numbers are used in their search algorithms (if they’re not already).
What I’m not sure is how this treats subscribers through feedburner feeds if you don’t have a feed on your domain. From what i can see the number in Webmaster tools is significantly less for me than what Feedburner reports my Google subscribers as (Google reports it at less than half what Feedburner does for Google subscriber numbers).
Via King Nomar