Notice how and where (bolded):
Starting today, advertisers in the beta will see an alert in their AdWords account informing them that they can now create pay-per-action campaigns. Going forward, advertisers who have enabled AdWords conversion tracking and received more than 500 conversions from their CPC and CPM-based campaigns in the past 30 days will be automatically added to the beta on a rolling basis.
Pay-per-action ads are only shown on publisher sites in the Google content network, also known as Google AdSense™ for content sites.