I agree that if the ownership is the same, then there is not a problem. I would hesitate to allow transfers to accounts where the ownership is not the same. A corporate account would be owned by the corporation, therefore, transfer to an individual's account would not be possible. By limiting transfers between accounts with the same ownership should take care of this problem. Sole proprietorships are not your concern--if they set them up with the same ownership, then the transfer would be allowed. Who cares if the sole proprietor is siphoning money from the company for personal use? He owns the business. Partnerships could pose a problem where you have two people in a partnership who think they are a proprietorship and opened the "partnership" account as a proprietorship account (happens all the time). Would the online banking allow the first person on the account transfer funds to their personal account? What about a husband and wife partnership? Would the online banking allow a business account with the H&W listed as owners to transfer to the H&W's personal account?
As you can tell, I do think there is reason for limiting transfers from an embezzlement standpoint. Different business types have different levels of risk.
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Better a patient man than a warrior, a man who controls his temper than one who takes a city