Somehow Paypal has started saying no to many PTC sites. So they are turning to Alertpay. However, I still find that many sites are still paying through Paypal but for that you are required to have a verified account. I think that they must have put the similar condition for the site owners also.
Anyway, it seems that due to paypal's refusal to deal with many ptc, alertpay is now being prefered more and more.