I think it's ego. I think it makes them seem bigger than they really are.
I don't think it's necessary. I'm perfectly happy to promote a single website that has no cash program. Just give me a ccbill sign up form where I can merge my pre-existing account and I'm thrilled.

In fact I'm less likely to sign up with a site that processes their own stuff and doesn't let the biller pay me. That means I more likely not to get paid.

Michael