I suspect the reason CCBill won't do ACH is, as Lee said, about the fees for wire transfers... but keep in mind that the vast majority of CCBill customers are pretty small sites, and probably don't get wire transfers.

This means that ccbill mails a check on Monday and at the earliest, it hits CCBill's bank on Wednseday or Thursday, so they can invest or use that money for other purposes for an extra several days. Given the really massive amount of money that's being discussed here (thousands upon thousands of sites) that interest, 2 or 3 days a week, amounts to almost a half-years' interest on whatever money is sent out in checks. This is probably a pretty significant revenue stream.