This boggles me as well, wordpress has a huge install base and them making a sanctioned plugin for these ads would give a much wider audience to advertisers. T

This boggles me as well, wordpress has a huge install base and them making a sanctioned plugin for these ads would give a much wider audience to advertisers. The only reason I can possibly see wordpress.com sites as the reason for the rollout is that they are doing a limited release in order to not get overwhelmed.