How would a generic account be any better than a credit card? How about a pre-paid credit card? Unless the account is usable for purchases other than porn, it will look just as odd on a credit card statement / bank transfer etc. Paypal is a mess as it is, and even still Checkout is doing a poor job of competing with it.
I also suspect 99c videos wouldn't be competitive with current products. If we're talking impulse purchases here, such that free porn clip sites aren't doing it, I think there's something else going on. Porn vendors have to walk a tightrope: show enough of what's available to encourage the purchase, but not so much that the customer gets satisfaction too early. I think the way they prod the customer over the line is by promising a lot in return for the commitment. And of course, they're betting that the commitment lasts longer than is in the customer's best interests.