Of course there is a security hole that can be used by anyone who knows how. But the truth is, they have only been exploited for jailbreaking and not really anything else. It would be clueless to think that Apple's main concerning regarding the platform's security right now isn't related to jailbreaking.
If they want to be accepted by the enterprise community AND if they want to add functionality like allowing us to make purchases in stores and on toll roads using RFID technology of our iPhones (once that comes along) then they need to make the devices more secure. They have to demonstrate that security before people will take the higher stakes risks.
Right now the holes are only being exploited for jailbreaking because there isn't a lot of incentive to do more. Once the prize has increased, the incentive will be there.