Paypal isn't available in some countries and swt probably lives in one of them, while on the other hand Payza accepts accounts from all countries. Also Payza's limit on unverified accounts is a lot more than the limitations imposed by Paypal.Paypal is free to use and generally accepted more places than Payza. Why not just make a paypal?
Yeah, and 99 percent of those clients would want to host illegal content, and attract DDoS attacks. I don't think Interserver wants to appeal to that crowd of people.