I think it's due to the interface. Think about it, though. Why re-invent the wheel? They might be separate companies that bought software from the same vendor. A vendor that sold one, showed it to the others, and they bought it.
Or, they might be the same company.
Either way, I bought some stuff here, and was pleased with the service and pricing. So I don't care.
1998 C230 "Black Betty"